Vibratory motors and methods of making and using same

ABSTRACT

A single piezoelectric is excited at a first frequency to cause two vibration modes in a resonator producing a first elliptical motion in a first direction at a selected contacting portion of the resonator that is placed in frictional engagement with a driven element to move the driven element in a first direction. A second frequency excites the same piezoelectric to cause two vibration modes of the resonator producing a second elliptical motion in a second direction at the selected contacting portion to move the driven element in a second direction. The piezoelectric is preloaded in compression by the resonator. Walls of the resonator are stressed past their yield point to maintain the preload. Specially shaped ends on the piezoelectric help preloading. The piezoelectric can send or receive vibratory signals through the driven element to or from sensors to determine the position of the driven element relative to the piezoelectric element or resonator. Conversely, the piezoelectric element can receive vibration or electrical signals passed through the driven element to determine the position of the driven element. The resonator is resiliently urged against the driven element, or vice versa. Plural resonators can drive common driven elements.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/691,362 filed Oct. 22, 2003 now U.S. Pat. No. 6,825,592, which is acontinuation application to U.S. patent application Ser. No. 09/801,194filed Mar. 8, 2001 now U.S. Pat. No. 6,870,304, which claims priorityunder 35 U.S.C. § 119(e) from U.S. Provisional Patent Application No.60/191,876 filed Mar. 23, 2000 entitled “Electric Motor Using Vibrationto Convert Electrical Energy Into Mechanical Motion” and listinginventors Bjoern Magnussen, Steve Schofield and Ben Hagemann; and fromapplication No. 60/215,438 filed Jun. 30, 2000, Application No.60/215,686 filed Jun. 30, 2000, Application No. 60/231,001 filed Sep. 8,2000, and Application No. 60/236,005 filed Sep. 27, 2000; each entitled“Electrical Motor Using Vibration to Convert Electrical Energy IntoMechanical Motion” and listing inventors Bjoern Magnussen, Ben Hagemannand Peter Varadi. The entire disclosures of these preceding applicationsare incorporated by this reference as though set forth fully herein.

BACKGROUND OF THE INVENTION

To move small components, electromagnetic motors are often used becausethey are relatively inexpensive. The electromagnetic motors rotate veryquickly and can only apply a low force, so they are always used with agearbox that provides the slower motion and increased power necessaryfor practical applications. It should be noted that the movement ofdriven elements referred to in this disclosure refers to a translationor rotary motion in a common direction, and does not included motionthat merely moves a part alternatively back and forth to shake the partwithout any net movement. While the conventional electromagnetic motorsare relatively inexpensive, there are a large number of moving partswhich complicates assembly and reliability, and the low power and needfor a gearbox not only limits their application but also makes the costexcessive for many applications. Moreover, these motors are too big, notvery precise in their motion, and are noisy. There is thus a need for asimpler, quieter and less expensive motor.

An alternative type of small motor is a piezoelectric motor, which usesa material that can change dimension when a voltage is applied to thematerial. Piezoelectric ceramics are used in electromechanicalmicromotors to provide linear or circular motion by making frictionalcontact between the vibratory motor and a driven object. Thesepiezoelectric motors are composed of at least one mechanical resonatorand at least one piezoelectric actuator. When electrically excited byoscillating electrical signals, the actuator generates mechanicalvibrations that are amplified by the resonator. When the resonator isbrought into contact with a body, these vibrations generate frictionalforces in the contact area with the body and cause the body to move. Thespeed, direction and mechanical power of the resulting mechanical outputdepend on the form and frequency of the vibrations in the contact area.These piezoelectric motors work with small changes in dimension for agiven voltage, and they can vibrate at many tens of thousands of cyclesper second. Various cumbersome and expensive designs have been used toobtain useful forces and motions from these small vibratory motions.

One type of piezoelectric motor is a traveling wave motor, which uses awave that travels through the piezoelectric material. These motorstypically are based on a disc shaped design and are expensive toproduce. The shape and the cost of these motors limit their application.

Other types of piezoelectric motors require a specially shaped waveformin the input signal in order to cause the piezoelectric material to movein a desired direction. One such type of motor is referred to as astick-slip drive. These motors have a piezoelectric element that movesan object in a desired direction on a support at a relatively slow ratesufficient to allow friction to move the object. The waveform applied tothe piezoelectric element causes the piezoelectric to then quicklyretract and effectively pull the support out from under the objectcausing the object to slip relative to the support. The process isrepeated, resulting in motion. Since these motors require a sawtooth orsimilar shaped waveform to operate, they require complex electronicsthat increase the cost of such motors.

A yet further type of piezoelectric motor is the impact drive, whichrepeatedly hits an object in order to make it move.

In piezoelectric micromotors, the piezoelectric element can be used toexcite two independent modes of vibration in the resonator. Each modecauses the contact area on the resonator to oscillate along a certaindirection. The modes are often selected so that the respectivedirections of oscillation are perpendicular to each other. Thesuperposition of the two perpendicular vibrations cause the contact areato move along curves known as Lissajous figures. For example, if bothvibrations have the same frequency and no relative phase shift betweenthe vibrations, the motion resulting from the superposition is linear.If the frequencies are the same and the relative phase shift is 90degrees, then the resulting motion is circular if the amplitudes of eachvibration are identical; otherwise the resulting motion is elliptical.If the frequencies are different, then other motions such asfigure-eights can be achieved.

The Lissajous figures have been used to produce figure-eight motiondrives. These drives require an electrical signal that has to containtwo frequencies to cause a tip of the vibration element to move in afigure-eight shaped motion. The resulting electronics are complex andexpensive, and it is difficult to use the figure-eight motion to createuseful motion of an object.

In order to move another body and to create a mechanical output,circular or large-angle elliptical motions (semi-axes nearly equal) havebeen preferred over linear motions, Piezoelectric micromotors in theprior art thus commonly employ two perpendicular modes of vibration thathave a relative phase shift of approximately ninety degrees. The modesare excited close to their respective resonance frequencies so that theresulting mechanical output is maximized. If the relative phase shiftbetween the two modes is changed to −90 degrees, the direction in whichthe ellipse is traversed is reversed. The motion of the body in contactwith the resonator is thus reversed as well. But these conventionalmotors require two piezoelectric drivers located and selected to excitethe two separate resonant modes. This requires two sets of drivers, twosets of electronic driving systems, an electronic system that willreverse the phase of each driver, and the basic design placeslimitations on the locations of components.

The prior art thus includes electromechanical micromotors where arod-like resonator has a small piezoelectric plate that is attached tothe resonator. The resonator contacts the moving body at the tip of therod. The actuator excites a longitudinal mode and a bending mode of therod. The excitation frequency is chosen in-between the two resonancefrequencies of the respective modes so that the relative phase shift is90 degrees. The phase shift is generated by the mechanical properties ofthe resonator, in particular its mechanical damping properties. Theresulting elliptical motion of the resonator's tip is such that one ofthe semi-axes of the ellipse is aligned with the rod-axis and the othersemi-axis of the ellipse is perpendicular thereto. A secondpiezoelectric actuator is used to reverse the direction in which theellipse is traversed, and is placed at a different location on theresonator. The second piezoelectric actuator is located in such a waythat it excites the same two modes but with a relative phase shift of−90 degrees.

Unfortunately, this actuator requires two sets of electronics to drivethe motor in opposing directions, and has two sets of drivingpiezoelectric plates, resulting not only in a large number of parts butalso greatly increasing the complexity of the system and resulting insignificant costs for these type of motors. The motor also has limitedpower because the driving frequency is selected to be between tworesonant frequencies. There is thus a need for a vibratory motor withsimpler electronics, fewer parts, and greater efficiency.

In other vibratory motors, a piezoelectric element has a number ofelectrodes placed on different portions of the element in order todistort the element in various ways. Thus, for example, two modes ofvibration can be excited by at least two separate, independently excitedelectrodes in each of four quadrants of a rectangular piezoelectricceramic element. A second set of electrodes is used to reverse thedirection in which the ellipse is traversed. The resulting ellipticalmotion is such that one of the semi-axes of the ellipse is aligned withthe longitudinal axis of the motor and the other semi-axes of theellipse is perpendicular thereto. As mentioned elsewhere, the ratio ofthe semi-axes can be advantageously used to increase motion or reducetravel time, by making advantageous use of ratios of 5:1, 10:1, or from20–50:1. Again though, there are a number of electronic connections andmany parts to achieve this motion, resulting in a high cost for thistype of motor. It is an object of some aspects of the present inventionto provide a micromotor, which is cheaper and easier to manufacture thanprevious art.

SUMMARY OF THE INVENTION

This invention uses a single piezoelectric element and a mechanicalresonator to achieve its desired motion. The piezoelectric element hasone pair of electrical contacts. The piezoelectric element is excitedusing sinusoidal electrical signals with the element, resonator, andsometimes the mounting system being configured so that at least twomodes of vibration are excited by the single signal to generate anelliptic motion in the area where the resonator comes into contact withthe body to be moved.

Unlike the prior art, the semi-axes of the ellipse advantageously areneither aligned with the longitudinal axis of the resonator nor in adirection perpendicular to it. Also, the relative phase shift betweenthe two modes need not be close to 90 degrees so as to produce acircular or nearly circular-elliptical path. The amplitudes of therespective vibrations can be different in magnitude. At a givenfrequency, the motor 26 (see FIG. 1) moves the body 42 in one direction.When operated at a different frequency, the motor 26 moves the body 42in a different direction or different rotation. Preferably, it moves thebody 42 in the opposite direction, but this will depend on the needs ofthe user and the design of the motor 26, its support, and the drivenbody 42. It is possible to operate the motor 26 at even more frequenciesto generate additional motions of the body such as rotation and/ortranslation of an axle. The movement of driven body 42 in thisdisclosure refers to a translation or rotary motion of the body 42 in acommon direction, rather than motion that merely moves the body 42alternatively back and forth in a cyclic path to shake the body withoutany net translation or net rotation.

According to the invention, a piezoelectric element is mounted inside amechanical resonator in part to preload the element in compression. Thecombined piezoelectric element and mechanical resonator are referred toas a motor or as a vibration element. The combined piezoelectric elementand resonator are configured so that a single driving frequency excitesat least two vibration modes sufficiently to cause an elliptical motionin a first direction at a predetermined point on the motor that is goingto be used to drive a driven object. In particular, a vibration mode istypically along the longitudinal axis of the motor, and a secondvibration mode is transverse thereto so as to result in bending ortorsion. The motion can be achieved by appropriately configuring theresonator and piezoelectric element, or in some cases by locating thedriving piezoelectric element offset from a longitudinal axis of theresonator to cause combined axial and bending motion.

The motion at a distal edge 44 at a distal end 36 of the resonator istypically greatest and is preferably used, although other locations onthe motor can be used in some specific embodiments. The opposing end ofthe motor is the proximal end 35. The result is the distal edge moves inan elliptical path resulting from a combination of at least twovibration modes when the motor is excited by a single signal at a firstfrequency. The motor is further configured such that a second drivingfrequency excites two resonant vibration modes in the motor so that thepredetermined point on the motor rotates in an elliptical path in anopposite direction as the first elliptical path. A single piezoelectricelement and resonator are thus driven by a single frequency to generatea first elliptical motion at a predetermined location on the vibratorymotor. The piezoelectric element is driven at a second frequency toexcite two resonant vibration modes of the vibratory motor that causethe predetermined location to move in a second elliptical motion in adifferent, and preferably opposite direction to the first ellipticalmotion, sufficient to move the driven element a desired distance. Thetwo elliptical motions are typically not overlapping. The motion can beachieved at various locations on the motor, in varying amplitudes anddirections, and that allows a variety of arrangements in which the motorcan drive other elements.

In accordance with the invention, the motor thus requires a singlepiezoelectric driver, a single resonator, and two separate frequenciesto move objects in two opposing directions. The selection andconfiguration of the piezoelectric driver and the resonator achieveresonance or near resonant vibrations of sufficient magnitude to moveobjects with predetermined force. The effort expended in the designresults in a motor of simple design, few parts, low cost and highefficiency.

In a further embodiment, the motor is resiliently urged toward thedriven object. Depending on the mounting arrangement, the mounting maybecome part of the vibrating mass and affect the resonant vibrationmodes of the motor in order to achieve the desired motion at the desiredlocation on the motor that is to be in contact with the driven object.

A simplified vibratory system is provided that has a source of vibrationin driving communication with a resonator that has a selected contactingportion located to engage the driven element during use of the system.The source of vibration is preferably a piezoelectric element, but couldcomprise other elements that convert electrical energy into physicalmotion, such as magnetostrictive or electrostrictive devices in somespecific embodiments. For convenience, a piezoelectric vibration sourcewill usually be used in this description.

The vibrating element and resonator are configured to move the selectedcontacting portion in a first elliptical motion when the resonator isexcited to simultaneously resonate in at least two vibration modes by afirst signal at a first frequency provided to the vibrating element,according to a specific embodiment. The resulting elliptical motion isof sufficient amplitude to move the driven element when the drivenelement and selected contacting portion are maintained in sufficientcontact to achieve movement of the driven element. The at least twovibration modes are selected so that at least one does not include apure longitudinal or bending mode of the resonator in order to producethe first elliptical motion. The movement of driven elements referred toin this disclosure refers to a translation or rotary motion in a commondirection, rather than motion that merely moves a part alternativelyback and forth to shake the part without any net translation or netrotation.

The piezoelectric element and resonator are preferably configured tocause the selected contacting portion to move in a second ellipticalmotion a desired amount when excited to simultaneously resonate in atleast two vibration modes by a second signal at a second frequencyprovided to the piezoelectric element, according to the specificembodiment. This allows multi-degree motion of the driven element by asingle vibrating element. Additional vibration modes excited bydifferent discrete frequencies can be used to provide different motionsto the same selected contacting portion, or to different selectedcontacting portions engaging different driven elements. In one versionof a preferred embodiment, the resonator comprises an elongated memberwith the selected contacting portion being located on an edge of adistal end of the member.

A number of variations on this basic combination are described, afterwhich some further features and advantages are discussed. One variationincludes having a resilient element interposed between a base and thevibratory element and located to resiliently urge the vibratory elementagainst the driven element during operation of the system. There areadvantages to having the vibration mode produce a node on the resonatorelement at the first frequency, with a resilient mounting connected tothe vibratory element at the node and located to resiliently urge thevibratory element against the driven element during operation of thesystem. The resilient mounting could also be connected to the vibratoryelement at a location other than the node yet still located toresiliently urge the vibratory element against the driven element duringoperation of the system. The resilient mounting can help determine thevarious vibration modes.

Advantageously, the piezoelectric element is held in compression in theresonator during operation of the system. Preferably, the piezoelectricelement is press-fit into an opening in the resonator to place thepiezoelectric element in compression during operation of the system.Further advantages of this press-fit can be achieved if thepiezoelectric element is held in compression by walls of the resonatorthat are stressed past their yield point, during operation of thesystem. Further advantages are derived by having the walls curved.Advantages are also provided if the piezoelectric element has aninclined surface adjacent an edge of the piezoelectric element to makeit easier to press-fit the piezoelectric element into an opening in theresonator.

The first and second elliptical motions each have a major and minoraxis, and there are advantages to having the ratio of the major to minoraxes of each elliptical motion being in the range of about 3:1 to 150:1,and preferably from about 4:1 to 30:1, and ideally from about 5:1 to15:1. Among other advantages, faster motion can be achieved, and thesystem design is easier to achieve. Advantageously, one of the major orminor axes is aligned with an axis of motion of the driven element inorder to maximize the motion, and preferably the major axis is aligned.

There are advantages to having the major axes of these ellipses inclinedat an angle with respect to a predominant axis of the vibratory element,and to maintain that inclination angle over a range of drivingfrequencies. There are thus advantages to having the systemconfiguration and angle of inclination selected so that an angle βbetween the major axis and a tangent to the driven element at theselected contacting portion and along the direction of motion, varies byabout 25 degrees or less over a frequency range of about 200 Hz orgreater, on either side of the first frequency. Advantageously the angleβ varies by about 10 degrees or less.

There are also advantages to having the angle vary in order to allowgreater ease in system design and to improve performance, among otherfactors. Thus, there are advantages to having a major axis of theelliptical motion inclined at an angle β, with the angle β being betweenabout 5–85 degrees when the selected contacting portion is drivinglyengaging the driven element. Most of these ranges omit the range whenthe angle β is between about 0–5 degrees, and that occurs when the sameselected contacting portion is used for multiple motions. But when theselected contacting portion achieves only one direction of motion of thedriven element, it is possible to more closely align the axes andachieve alignments within about 0–5 degrees of the driven motion.

Another feature of this invention is the ability to achieve the desiredmotion over a range of driving frequencies in a manner that allows theuse of components with lower tolerances and thus lower costs. Thus thereis provided a vibratory element having a source of vibration vibrating aresonator to amplify the vibration. The resonator has a selectedcontacting portion located to engage a driven element to move the drivenelement along a driven path during use of the vibratory element. Theselected contacting portion moves in a first elliptical path when thesource of vibration is excited by a first electrical signal at a firstfrequency. The elliptical path has a major and minor axis which are notaligned with a predominant axis of the vibrating element by a definedangle that varies by less than about 10 degrees when the first frequencyvaries by about 200 Hz or more on either side of the first frequency.Preferably the defined angles vary by less than 5 degrees when the firstfrequency varies by 200 Hz, and desirably when the first frequencyvaries by 2.5 kHz, or more.

The other features of this invention can also be used with this range ofdriving frequencies. Thus, as before, the source of vibration ispreferably a piezoelectric element, but other elements could be used.The motion can be caused by pure vibration modes or by at least twovibration modes that are superimposed, but preferably at least one ofthe vibration modes is not a pure longitudinal mode or pure bendingmode. Advantageously the vibratory element is connected to a resilientsupport located to resiliently urge the selected contacting portionagainst a driven element during use of the vibratory element. Asdesired, the resilient support can be used to help define the vibrationmodes generating the elliptical motion.

Another aspect of this invention comprises a vibratory component formoving a driven element using off-resonance vibration modes. Thevibratory component includes a vibratory element, such as apiezoelectric vibration source, mounted to a resonator to form avibrating element. The vibrating element has a selected contactingportion located to engage the driven element during use. A variety ofpiezoelectric vibration sources can be used, including pluralpiezoelectric elements to achieve the desired elliptical motion of theselected contacting portion. But preferably the selected contactingportion moving in a first elliptical path has a major axis and minoraxis when the vibration source is excited by a first electrical signalthat causes at least two vibration modes superimposed to create thefirst elliptical path. Advantageously at least one of the vibrationmodes is other than a pure longitudinal mode and other than a purebending mode. Further, for this particular aspect, at least one of theat least two vibration modes is off-resonance, with the first electricalsignal being amplified sufficiently to cause the at least oneoff-resonance vibration mode to produce a motion of the selectedcontacting portion having sufficient amplitude that the resultingelliptical path can move the driven element during use. Thisoff-resonance feature can be used with other features described herein,including the resilient support, press-fit piezoelectric elements, andother features to name a few.

One feature not mentioned earlier but applicable to the variousembodiments and features of this invention is the use of a large aspectratio on the elliptical motion of the selected contacting portion. Theratio of the major axis to the minor axis is preferably about 5:1 orgreater, with ratios of 15:1 and 30:1 believed to provide usable butprogressively less desirable motion. As the aspect ratio increases, thedriving motion becomes more akin to an impact drive. Nevertheless, it isbelieved possible to have aspect ratios of 3:1–150:1, or even more,provide usable motion using the various features and embodiments of thisdisclosure.

One further aspect of this invention is the use of vibration modes otherthan pure longitudinal or pure bending. Thus, the invention includes avibration source mounted to a resonator to form a vibrating element. Thevibrating element has a selected contacting portion located to engagethe driven element during use. The selected contacting portion moves ina first elliptical path having a major axis and minor axis when thevibration source is excited by a first electrical signal that causes atleast two vibration modes that are superimposed to create the firstelliptical path. In this particular aspect, at least one of thevibration modes is other than a pure longitudinal mode and other than apure bending mode. The elliptical motion has a major axis and minoraxis, one of which is aligned with the first direction an amountsufficient to cause motion of the driven element. Stated differently,the vibratory element moves the selected contacting portion in first andsecond elliptical paths each having a major and minor axis. At least oneof the major and minor axes does not coincide with the direction ofmotion resulting from the elliptical path with which the axis isassociated. This use of vibration modes other than pure bending or purelongitudinal can be used with other features described herein, includingthe resilient support, press-fit piezoelectric elements, and otherfeatures to name a few.

Another aspect of this invention is the use of elliptical motion thatdoes not align with the vibration element, but rather uses an inclineddriving element and driven element. There is thus provided a vibratorysystem for moving a driven element that includes a driven elementmovable in at least a first direction. The vibration source is mountedto a resonator to form a vibrating element; the vibrating element havinga selected contacting portion located to engage and move the drivenelement. For this particular aspect, the selected contacting portionmoves in a first elliptical path having a major axis and minor axis atleast one of which is not aligned with a longitudinal axis of thevibrating element. Advantageously, the longitudinal axis is inclined atan angle α to a tangent to the driven element in the first direction atthe selected contacting portion. The angle α is between about 10 and 80degrees when the selected contacting portion is drivingly engaging thedriven element. That angle is further refined as discussed later. Thisuse of the inclined axis can also be used with other features describedherein, including the resilient support, press-fit piezoelectricelements, and other features to name a few.

This invention also comprises methods for implementing the aboveapparatus and advantages. In particular, it includes a method ofconfiguring a vibratory system having a vibrating element with aselected contacting portion drivingly engaging a driven element to movethe driven element by moving the selected contacting portion in a firstelliptical motion. The method comprises analyzing that elliptical motionin a localized coordinate system in which at least one of the major andminor axes of the elliptical motion are not aligned with a predominantaxis of motion of the vibrating element. The method then varies thesystem design to incline at least one of the elliptical axes relative toa tangent to the driven element in the direction of motion at theselected contacting portion to more closely align at least one axis withthe tangent by an amount sufficient to achieve acceptable motion of thedriven element. The inclination is achieved by altering the ellipticalmotion or altering the relative orientation of the vibrating element andthe driven element, or both. That inclination is maintained duringoperation of the vibrating system.

There are advantages to orienting the localized coordinate systemrelative to the tangent. There are further advantages in setting theangle of inclination of the major axis of the first elliptical motion,designated by an angle β₁, to an angle that is greater than 5 degrees,and with the vibrating element and the driven element being inclinedrelative to each other by an angle α that is greater than about 5degrees.

The method also can include the provision of a vibrating element havingthe selected contacting portion moving in a second elliptical motion tomove the driven element in a second direction a desired amount. Afurther variation of this method is to analyze that second ellipticalmotion in a similar method to the first elliptical motion. Thus, thesecond elliptical motion is analyzed in a localized coordinate system inwhich at least one of the major and minor axes of the second ellipticalmotion are not aligned with a predominant axis of motion of thevibrating element. The system design is altered to incline at least oneof the second elliptical axes relative to a tangent to the drivenelement in the second direction at the selected contacting portion tomore closely align the at least one axis of the second elliptical motionwith the tangent in the second direction by an amount sufficient toachieve acceptable motion of the driven element in the second direction.It is advantageous to maintain that inclination of the second ellipticalaxis during use of the system. The orientation of at least one of thefirst and second elliptical axes is typically a compromise that isselected to achieve less than optimum motion of the driven element inone direction in order to improve the motion of the driven element inthe other direction.

The method of analysis can also orient the localized coordinate systemrelative to the tangent, with the angle of inclination of the major axisof the first elliptical motion being designated by an angle β₁, and withthe vibrating element and the driven element being inclined relative toeach other by an angle α that is greater than about 5 degrees. The angleof inclination of the major axis of the second elliptical motion can bedesignated by an angle β₂, with at least one of β₁ and β₂ being greaterthan 5 degrees. Preferably, at least one of the angles β₁ and β₂ isbetween about 5–85 degrees. Moreover, in this method the vibratoryelement can be resiliently mounted to a base. The other featuresdiscussed herein could be used as well.

This invention allows the use of simplified driving systems. One drivingsystem uses an inductive coil mounted on the piezoelectric element andacting in cooperation with the inherent capacitance of the piezoelectricelement to form an L-C driving circuit. The wire coil can be integratedinto the vibratory element with the coil wire being also used as anelectrical connection to the vibratory element, either in series orparallel.

This invention also allows the use of a simple driver apparatus tocontrol the operation of the vibrating element and its mechanicalresonator when the vibrating element has an inherent capacitance. Asmentioned, the piezoelectric element has an inherent capacitance. Thecontrol apparatus has at least one switching element allowing theapplication of a predetermined signal, such as the sinusoidal signaldiscussed herein. Further, there is at least one electrical resonatordriver circuit driving the vibrating element, where the driver circuitis electrically coupled to and activated by the switching element.Finally, there is at least one inductive coil electrically coupled tothe vibrating element to form an electric resonator together with thecapacitance of the vibrating element so the signal excites the drivercircuit at a predetermined frequency. The circuit resonances areselected to produce with the first and second signals at the first andsecond frequencies used to generate the first and second (and other)elliptical motions.

There are advantages if the coil is either mounted to the vibratoryelement or mounted to a common support with the vibratory element.Preferably the coil encircles a portion of the piezoelectric element orthe mechanical resonator. Further, it is useful to locate the drivercircuit and switching element more than four times further away from thepiezoelectric element than the coil. To make the construction evensimpler, the same electrical conductor that is used to form the coil canalso connect the piezoelectric element to the driver circuit—either inparallel or series.

Moreover, in a further embodiment there is provided a piezoelectricresonator driver circuit having a plurality of unidirectional electricalgates to drive the piezoelectric element. The driver circuit iselectrically coupled to and controlled by the control element; thepiezoelectric element being electrically coupled to and paired with oneof the unidirectional gates. At least one electromagnetic storageelement, such as an inductive coil, is electrically coupled to thepiezoelectric element so that the electromagnetic storage element formsan electric resonator together with the capacitance of the vibratingelement. The unidirectional electrical gates can take the form of one ormore diodes arranged to prevent a negative electrical voltage to thepiezoelectric element. The driver circuit preferably resonates at amodulated predetermined first resonant frequency selected to cause thevibrating element to cause the selected contacting portion to move inthe first elliptical motion with sufficient amplitude to move the drivenelement in the first direction when the selected contacting portionengages the driven element. The driver circuit also preferably resonatesat a modulated predetermined second resonant frequency selected to causethe vibrating element to cause the selected contacting portion to movein a second elliptical motion with sufficient amplitude to move a drivenelement in the second direction when the selected contacting portionengages the driven element. Moreover, a resistor can be electricallycoupled with the inductor and piezoelectric element and/or the gateelement to maintain an input voltage to the piezoelectric element withinpredetermined operating parameters. Advantageously the diode(s) arecoupled to the resistor in an orientation to prevent a negative voltagein the piezoelectric element.

The control methods achieved by the control circuits broadly includeplacing a control element in electrical communication with thepiezoelectric element and an inductor to alternate the electric signalbetween the inductor and piezoelectric element, with the piezoelectricelement providing a capacitance to function as a switched resonance L-Ccircuit so the electrical signal can resonantly drive the vibratingelement at a first frequency. Advantageously a portion of the inductoris formed on the resonator.

Further, the method for controlling the operation of the vibratingelement includes placing the control element in electrical communicationwith the piezoelectric element and the inductor to alternate theelectric signal between the inductor and piezoelectric element, with thepiezoelectric element providing a capacitance to function as a switchedresonance L-C circuit so the electrical signal can resonantly drive thevibrating element at a first frequency. Preferably, the method furtherincludes selecting the first frequency and configuring the vibratingelement to cause a selected contacting portion of the vibrating elementto move in a first elliptical path with sufficient amplitude to move adriven element in a first direction when the selected contacting portionengages the driven element.

Advantageously, the voltage to drive the piezoelectric element at thefirst frequency is greater than the supply voltage to the circuit.Moreover, the method includes placing a resistor in electricalcommunication with the piezoelectric element to shape the electricalsignal provided to the piezoelectric element. Further, the methodpreferably forms, at least a portion of the inductor around a portion ofthe vibratory element. Finally, the inductor and piezoelectric elementpreferably provide a capacitance to function as a switched resonance L-Ccircuit so that a second electrical signal can resonantly drive thevibrating element at a second frequency, with the second frequency beingselected in conjunction with the configuration of the vibratory elementand its mounting to cause the selected contacting portion of thevibrating element to move in a second elliptical path with sufficientamplitude to move the driven element in a second direction when theselected contacting portion engages the driven element.

This invention also includes a method of configuring a vibratory systemfor moving a driven element that is supported to allow the drivenelement to move in a predetermined manner at a predetermined rate oftravel with a predetermined force. The system has a selected contactingportion of a vibratory element periodically engaging the driven elementto move the driven element, with one of the selected contacting portionand the driven element being resiliently urged against the other of theplaced in resilient contact with the selected contacting portion and thedriven element. The resilient contact is provided by a resilientsupport, with the vibratory element being caused to vibrate by avibration source that converts electrical energy directly into physicalmotion. The vibratory element includes the vibration source mounted in aresonator with the selected contacting portion being on the resonator.

The method of configuring this system comprises defining a desiredelliptical motion of the selected contacting portion to produce adesired movement of the driven element. At least one of the vibratoryelement and the resilient support is configured to cause the resonatorto vibrate in two modes of sufficient amplitude and phase that theselected contacting portion moves in an elliptical path when thevibratory source is excited by a first signal at a first frequencyprovided to the vibration source. The elliptical path is sufficientlyclose to the desired elliptical motion to achieve an acceptable motionof the driven element.

The method can further comprise defining a second desired ellipticalmotion of the selected contacting portion to produce a second desiredmovement of the driven element. At least one of the vibratory elementand the resilient support is configured to cause the resonator tovibrate in two modes of sufficient amplitude and phase that the selectedcontacting portion moves in a second elliptical path when the vibratorysource is excited by a second signal at a second frequency provided tothe vibration source. The second elliptical path is selected to besufficiently close to the second desired elliptical motion to achieve anacceptable second movement of the driven element. The vibration sourceis preferably selected to comprise a piezoelectric element. Further, theresonator can be configured to cause the desired motion of the selectedcontacting portion, or the resonator in combination with a resilientsupport can be configured to cause the desired motion.

In addition to the selected contacting portion moving the driven elementin a first direction when the source of vibration is driven by the firstsignal and moving the driven element in a second direction when thesource of vibration is driven by the second signal, advantages arise ifthe selected contacting portion further moves in the first directionwhen a single sinusoidal signal of a first frequency is applied, and canalso move in the first direction when the first frequency is dominantand superimposed with plural sinusoidal signals of differentfrequencies. In these latter instances, the second signal does not occursimultaneously with the first signal or else the first and secondsignals are of substantially different amplitude if they do occursimultaneously.

The method further includes placing the piezoelectric element incompression in the resonator during operation of the system bypress-fitting the piezoelectric element into an opening in theresonator. This is preferably achieved by stressing walls of theresonator past their yield point but not past their ultimate strengthpoint. The method further includes interposing a resilient elementbetween the base and the vibratory element to resiliently urge thevibratory element against the driven element during excitation at thefirst frequency. Further methods to implement the above features andadvantages are disclosed in more detail below.

A further method of this invention includes a method for moving objectsusing vibratory motors having a vibration source placed in a resonator.The method comprises moving a selected contacting portion of a resonatorin a first elliptical motion in a first direction by configuring theresonator to simultaneously vibrate in two modes of sufficient amplitudeand phase to cause the first elliptical motion of the selectedcontacting portion when a single electrical signal is applied to thevibration source. The method can further comprise placing the selectedcontacting portion in resilient contact with a driven element to movethe driven element. Additionally, the method can further compriseconnecting a resilient element to the resonator to resiliently urge theresonator against a driven element.

Other aspects of this method include selecting a piezoelectric elementfor the vibration source and placing that piezoelectric element incompression by press fitting it into an opening in the resonator. Theopening is preferably defined by at least two opposing walls that arestressed beyond their elastic limit when the piezoelectric element ispress-fit into the opening. There are advantages if the walls areselected to be curved.

When a piezoelectric element is used for the vibration source, theinherent capacitance of the piezoelectric lends itself to the use ofsimplified control systems while still maintaining system performance. Acontrol switch can activate a resonator driver circuit driving thevibrating element, with at least one electromagnetic storage element,such as an inductive coil, electrically coupled to the vibrating elementto drive the vibrating element when the driver circuit is activated. Thevibrating element increases charge when the electromagnetic storageelement discharges and the coil increases its charge when the vibratingelement discharges and the driver circuit is not activating thevibrating element. This construction basically places a control elementin electrical communication with the piezoelectric element and aninductor to alternate the electric signal between the inductor andpiezoelectric element, with the piezoelectric element providing acapacitance to function as a switched resonance L-C circuit so theelectrical signal can resonantly drive the vibrating element at a firstfrequency selected to achieve the desired elliptical motion at theselected contacting portion. This allows the voltage to drive thepiezoelectric element at the first frequency to be greater than thevoltage of the electrical signal provided to the control element. Thesame circuit can be used to provide the electrical signal for othervibration modes of the piezoelectric element.

Further, the coil can be mounted to the vibratory element or mounted tothe same support as the vibratory element. Advantageously, the coil canencircle a portion of the vibratory element. Moreover, the coil can beconnected to the piezoelectric element in series, or in parallel.Additionally, the piezoelectric driver circuit can have a plurality ofunidirectional electrical gates, such as a diode, can be paired with thepiezoelectric element to prevent or at least limit any negative voltageto the piezoelectric element. In these driver circuits, the frequency isselected to achieve the desired motion of the selected contactingportion.

This invention further includes improved manufacturing and assemblyaspects for vibratory apparatus used to move a driven element. In theseaspects a vibration source is used that converts electrical energydirectly into physical motion. A resonator is provided having an openingdefined by at least two opposing sidewalls that are stressed beyondtheir elastic limit to hold the vibration element in compression. Thevibration source is within that opening so that the vibration element isheld in compression by the resonator under a defined preload duringoperation. Advantageously, the vibration source is press-fit into theopening, and comprises a piezoelectric element. Further advantages areachieved if the sidewalls are curved.

Moreover, it is useful to provide the piezoelectric element with atleast two opposing edges that are inclined and located to engage edgesof the opening to make it easier to press-fit the piezoelectric elementinto the opening while reducing damage to the piezoelectric element. Thereduction of damage is especially desirable in view of the damage thatcan occur to the piezoelectric element and to the resonator if theinclined edges are absent. Preferably, there are at least two opposingedges that have surfaces substantially parallel to the abutting wallsdefining the opening, and an inclined surface extending therefrom to acontacting surface abutting one of the walls, with the contactingsurface exerting the preload.

In one embodiment, a resonator has a longitudinal axis with an openingpartially defined by two sidewalls on opposing sides of the longitudinalaxis and two opposing end walls on the longitudinal axis. Apiezoelectric element is held in compression by the opposing end walls,with each of the sidewalls being stressed beyond its elastic limit tohold the piezoelectric element in compression. The resonator has aselected contacting portion, which moves in a first elliptical motionwhen the piezoelectric element is excited by the various electricalsignals described herein. There are advantages if the sidewalls arecurved, and if at least one of the end walls or two opposing sides ofthe piezoelectric element that engage the end walls have edges that areinclined to facilitate press-fitting the piezoelectric element into theopening and wherein the piezoelectric element is press-fit between theend walls. The sidewalls can be curved to bow away from thepiezoelectric element, or toward the piezoelectric element. Further, aportion of an elastic element for supporting the resonator can beinterposed between one of the end walls and the piezoelectric element.

The invention also includes a method of placing a piezoelectric elementin compression in a resonator, where the resonator has end walls andsidewalls defining an opening sized to receive and place thepiezoelectric element in compression. The method includes increasing thedistance between opposing end walls enough to allow the piezoelectricelement to be forced between the end walls with a force that by itselfcould not force the piezoelectric element between the end walls in theoriginal state of the opening, and thereby placing the piezoelectricelement in compression while also stressing the sidewalls beyond theirelastic limit. The method can further include providing an inclinedsurface on at least one of either the end walls or the correspondingedges of the piezoelectric element, and forcing the piezoelectricelement into the opening by engaging said at least one inclined surface.

Moreover, the method can include pulling the opposing end walls apartwhile forcing the piezoelectric element into the opening. In one furtherembodiment, the method includes curving the sidewalls away from eachother, and urging the opposing, curved sidewalls toward each other inorder to move the end walls away from each other and then placing thepiezoelectric element between the end walls. In another embodiment, themethod includes curving the sidewalls toward each other, and urging theopposing, curved sidewalls away from each other in order to move the endwalls away from each other and then forcing the piezoelectric elementbetween the end walls. The various methods can also include interposinga resilient mount for the piezoelectric element between thepiezoelectric element and one of the end walls.

There is also advantageously provided a piezoelectric element configuredto be press-fit into an opening in a resonator. The opening is definedby sidewalls located on opposing sides of a longitudinal axis throughthe opening and separated by a first dimension, with opposing end wallslocated on the longitudinal axis and separated by a second dimension.The piezoelectric element has a first dimension that is smaller than thefirst dimension of the opening and has a second dimension larger thanthe second dimension of the opening and selected to stress the sidewallsbeyond their elastic limit when the piezoelectric element is insertedinto the opening. The piezoelectric element has inclined edgescorresponding in location to edges of the end walls when thepiezoelectric element is aligned to be inserted into the opening. Theabove variations can also be used with this embodiment, including curvedsidewalls, a resilient support for the resonator interposed between oneend wall and the piezoelectric element during use, and at least oneinclined edge corresponding in location to an edge of the end wall whenthe piezoelectric element is aligned to be inserted into the opening.

There is also advantageously provided a resonator 24 for use with apiezoelectric actuator. The resonator has a continuous walled,externally accessible opening sized to receive a piezoelectric elementor other source of vibration, and to hold that element in compression.The opening is optionally, but preferably defined in part by opposingsidewalls that are curved. The walls can be curved toward, or away fromthe opening and the piezoelectric element therein. Preferably thesidewalls are curved, and have a uniform cross section for a substantialportion of the length of the sidewall. A substantial length includesover half the length, preferably more, and ideally the entire lengthuntil the junction with the end walls is reached. Rectangular crosssections are preferred.

Given the present disclosure, further methods will be apparent to oneskilled in the art to implement the above features and advantages, andthe features and advantages discussed below. Further, other objects andfeatures of the invention will become apparent from consideration of thefollowing description taken in connection with the accompanyingdrawings, in which like numbers refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a plan side view of a first embodiment of this invention;

FIG. 2 shows a top view of the vibratory element of FIG. 1;

FIG. 3 shows an end view of FIG. 2;

FIG. 4 shows a perspective view of a second embodiment of thisinvention;

FIG. 5 shows a side view of a third embodiment of this invention using aC-clamp configuration;

FIG. 6 shows a perspective view of a fourth embodiment of this inventiondriving multiple elements;

FIG. 7 a shows a perspective view of a vibratory element of thisinvention containing a press-fit piezoelectric element;

FIG. 7 b shows an enlarged portion of the vibratory element of FIG. 7 aduring assembly;

FIG. 8 shows a fifth embodiment of this invention having a press-fitpiezoelectric element;

FIG. 9 shows a top view of a press-fit embodiment before deformation;

FIG. 10 shows a top view of the embodiment of FIG. 9 after deformationby a cylindrical wedge;

FIG. 11 shows a sectional view along line 11—11 of FIG. 10;

FIG. 12 shows a top view of an alternative embodiment of FIG. 9 using arectangular wedge;

FIG. 13 shows an embodiment with the piezoelectric element offset fromthe axis of a resonator;

FIG. 14 shows an embodiment with an insert offsetting the force from thepiezoelectric element from the centerline of a resonator;

FIG. 15 shows an embodiment with the piezoelectric element skewedrelative to the axis of the resonator;

FIG. 16 shows an embodiment with the piezoelectric element positionedbetween selectably positioned inert elements and compressed by athreaded fastener;

FIGS. 17–19 show suspension configurations for a vibratory element ofthis invention having a pivoted support for the vibratory element;

FIGS. 20–21 show suspension configurations for a vibratory element ofthis invention having a resilient support;

FIG. 22 shows a suspension configuration for a vibratory element of thisinvention having a pivoted support;

FIGS. 23–24 show configurations of a vibratory element and drivenelement of this invention with the longitudinal axes of the parts inparallel but offset planes;

FIG. 25 shows a configuration of a vibratory element and driven elementof this invention with the axes of the parts inclined at an angle;

FIG. 26 is an end view of the configuration of FIG. 25;

FIGS. 27–29 show configurations of two vibratory elements located inparallel but offset planes relative to the plane of the driven element;

FIG. 30 shows a configuration of two vibratory elements located in thesame plane but offset from the plane containing the driven element;

FIG. 31 shows a configuration of two vibratory elements and one drivenelement with the driven elements located above and below the drivenelement and at inclined angles relative to the driven element and facingeach other;

FIG. 32 shows a configuration of two vibratory elements and one drivenelement with the driven elements located above and below the drivenelement and at inclined angles relative to the driven element and facingthe same direction;

FIG. 33 shows a configuration of two vibratory elements and one drivenelement with the driven elements located on one common side of drivenelement and at inclined angles relative to the driven element and facingthe same direction;

FIG. 34 shows a configuration of two vibratory elements and one drivenelement with the driven elements located on one common side of thedriven element and at inclined angles relative to the driven element andfacing each other;

FIG. 35 shows a configuration of two vibratory elements and one drivenelement with the driven elements located on opposing sides of the drivenelement and at inclined angles relative to the driven element and facingthe same direction;

FIG. 36 is an end view of the configuration of FIG. 35;

FIGS. 37–40 show configurations of three vibratory elements and onedriven element;

FIG. 41 shows a front view of a configuration of six vibratory elementsand one driven element;

FIG. 42 shows a left side view of the configuration of FIG. 41;

FIG. 43 shows a diagram of the elliptical motion of the selected contactportion of this invention;

FIGS. 44–51 show graphical presentations of various aspects affectingthe elliptical motion of the contacting portion depicted in FIG. 43;

FIG. 52 shows a perspective view of a vibratory element having a slot inthe resonator in the same face of the resonator in which the opening isformed to receive the piezoelectric element;

FIG. 53 shows a perspective view of a vibratory element having a slot inthe resonator and an opening with curved ends to receive thepiezoelectric element;

FIG. 54 shows a perspective view of a vibratory element having a widerslot in the resonator;

FIG. 55 shows a perspective view of a vibratory element having a slot inthe resonator in a face of the resonator that is different from theopening formed to receive the piezoelectric element;

FIG. 56 shows a perspective view of a vibratory element having an “H”shaped opening to receive the piezoelectric element;

FIG. 57 shows a perspective view of a vibratory element having a slotdefining two beams in the resonator with the piezoelectric element beinglocated in one beam;

FIG. 58 shows a perspective view of a vibratory element having a hole inthe resonator to alter the performance of the vibratory element;

FIG. 59 shows a perspective view of a vibratory element having anenlarged mass at a proximal end of the resonator;

FIG. 60 shows a perspective view of a vibratory element having foursidewalls defining the opening in which the piezoelectric element isplaced;

FIG. 61 is a cross sectional view of a vibratory element enclosing thepiezoelectric element in a cavity within the resonator;

FIG. 62 is a side view of a vibratory element having several selectedcontacting portions to engage a driven element;

FIGS. 63–66 are electrical schematics for systems to provide electronicsignals to the vibratory elements of this invention;

FIG. 67 is a plan side view of a piezoelectric element having speciallyconfigured ends;

FIG. 68 is a perspective view of the piezoelectric element of FIG. 67;

FIG. 69 is a side sectional view of a die used to form the piezoelectricelements of FIGS. 67–68;

FIG. 70 is a schematic view of a vibrating driving element and avibrating driven element of a further embodiment of this invention;

FIGS. 71–72 are schematic views of several positioning sensingconfigurations;

FIG. 73 shows cross-sections for resonator elements of this invention;

FIG. 74 shows a schematic view of a vibrating element with a curvedspring suspension system;

FIG. 75 shows a sequence for press-fitting a piezoelectric into anopening in a resonator;

FIG. 76 shows a pull-fit process for a piezoelectric motor assembly ofthis invention;

FIG. 77 shows a further embodiment of a piezoelectric motor assembly ofthis invention;

FIGS. 78–80 show further embodiments in which a coil is integrated withor associated with the motor or motor components of this invention; and

FIG. 81 shows the motion of a selected contacting portion of thisinvention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Several embodiments of the motor of this invention will be described,following which a number of theoretical and practical operational anddesign aspects of the motors are described. Referring to FIGS. 1–3, andas described in detail at various locations, the piezoelectric motorassembly 20 has an element that converts electrical energy intomacroscopic mechanical motion. This is achieved by using a singleelectrical signal to generate at least two vibration motions at apredetermined location of a vibration element. The at least twovibration motions result in an elliptical motion at the predeterminedlocation. The elliptical motion is selected to cause the vibratingelement to engage a driven element during a time corresponding to atleast a portion of travel in direction of a long axis of the ellipse,and to disengage or slide over the driven element during a timecorresponding to travel in the opposite direction. A second, singlefrequency results in a second elliptical motion in an opposing directionto move the driven element in an opposing direction. The desired motionis used to determine the elliptical motion needed, and the variouscomponents of the system are designed to achieve that motion. The use ofa single frequency to generate elliptical motion and the simplicity ofthe resulting design allow a low cost, high reliability motor.

The motor assembly 20 has a vibration source 22 that converts electricalenergy directly into physical motion. The vibration source 22 ispreferably a piezoelectric element and comprises a block ofpiezoelectric material, or a multi-layer piezoelectric so that themotion of the various elements combine to increase the movement indesired directions. The shape of the piezoelectric 22 can vary, but itadvantageously has a longitudinal axis 25 along its direction ofgreatest motion. The piezoelectric 22 is mounted to, and preferablyinside, a resonator 24. The piezoelectric 22 and resonator 24 comprise avibration element 26 or motor 26.

The piezoelectric material is preferred because it reacts quickly toapplied voltages. While the resulting deflection for a given voltage issmall, about 0.1% or less of the length of the piezoelectric, andsmaller in other directions, the resulting force is large so thatvibration resonance can be achieved.

The source 22 can also comprise electrostrictive materials,magneto-restrictve materials (e.g., Terfenol), or other materials thatcan be used to excite vibrations, according to other embodiments.Preferably, the vibration source 22 comprises materials or devices thatconvert electrical energy directly into physical motion. For ease ofreference, the vibration source 22 will be referred to and describedherein as piezoelectric 22.

To avoid confusion between motor 26 and motor assembly 20, theterminology “vibration element” 26 will be used in most cases to referto the combination of the piezoelectric element 22 and the resonator 24.

The resonator 24 can have various shapes, but is illustrated as having arectangular shape with a rectangular cross-section. In order to mountthe piezoelectric 22 inside the resonator 24, it is useful to form acavity or an opening 28 in the resonator 24 to hold the piezoelectricelement 22. The opening 28 is shown as extending entirely through aportion of the resonator 24 to form a rectangular opening, withsidewalls 29 which define the sides of opening 28, the sidewalls beinglocated on opposing sides of the longitudinal axis extending through theopening 28, and with end walls 31 being located on the longitudinal axisextending through the opening 28. The opening 28 is thus advantageouslydefined by continuous walls that enclose the opening. Appropriateelectrical connections are provided to the piezoelectric 22 and maycomprise electrical connections of various types, but which areillustrated as wires 30.

Application of large voltages to an unrestrained piezoelectric 22 candamage the piezoelectric. Thus, the piezoelectric 22 is advantageouslyplaced in compression along at least its longitudinal axis, by end walls31. This also causes a preload, which optimizes the piezoelectriclifetime and performance. But a compressive force is not necessarilyused if other vibration sources are used that do not requirecompression, or that do not benefit from compression. Several ways topreload the piezoelectric element 22 are discussed later.

In order to make it easier to place the piezoelectric element 22 incompression, the opening 28 is advantageously enclosed on opposingsides, and preferably enclosed on opposing ends of the longitudinal axisof piezoelectric 22. This arrangement provides opposing surfaces thatcan be used to provide compression to the piezoelectric 22. One way topreload the piezoelectric 22 is by movably extending a screw 32 througha threaded opening in the proximal end 35 of resonator 24 so that adistal end of the screw can be moved to compress the piezoelectric 22against one end of the opening 28 in the resonator 24. Since thepiezoelectric material is brittle, a protective cap 34 is interposedbetween the distal end of the screw 32 and the adjacent end of thepiezoelectric 22. The cap 34 is made of a protective material thatallows the rotation of the screw 32 to compress the piezoelectric whilenot breaking or cracking the piezoelectric 22. Metal caps 34 arepreferred, but some lubricant or rotational accommodating design isadvantageously provided in order to avoid at least some damage to thepiezoelectric 22 from rotation of the screw 32. Other clamping methodsof the piezoelectric 22 without a screw and/or a protecting plate can beused, such as expansion or shrinkage of the opening 28. Additional waysare described below, and other ways will become known to those skilledin the art given the present disclosure.

When a voltage is applied to the piezoelectric element 22, thepiezoelectric element extends along longitudinal axis 25, and thatcauses the vibration element 26 to also extend in length, in part byelongating the smaller cross-section sidewalls 29. The vibration of thepiezoelectric 22 excites a longitudinal mode in the vibration element 26which causes the distal end 36 opposite the screw 32 to move back andforth along the longitudinal axis 25. In addition to that longitudinalmotion, bending modes of the vibration element 26 will be excited whichare transverse to the longitudinal axis 25. For the illustratedembodiment, a first preferred bending mode occurs in the directionindicated by arrow 38, which is perpendicular to the longitudinal axis25 in the plane of the paper on which the illustration is placed inFIG. 1. A second, preferred lateral bending mode occurs along an axisorthogonal to the paper on which the illustration is placed in FIG. 1,and is denoted by axis 40. In practice, the vibration modes are oftencombinations of various modes involving motion along and rotation aboutmultiple axes.

Advantageously, the components of the invention are configured so thatthe various modes are excited at or very close to their respectiveresonance frequencies in order to increase the amplitude of motion alongthe longitudinal axis 25 and preferably only one of the lateral axes 38,40. As discussed later, the lateral bending can be excited either byasymmetrical placement of the piezoelectric 22 relative to the resonator24, or by an asymmetrically placed mass on the vibration element 26, orby a mounting of the piezoelectric element 22, or by shaping theresonator 24 to resonate with a desired lateral motion, or by othermechanisms, some of which are discussed later.

In the embodiment depicted in FIGS. 1–2, the motion along lateral axis38 is preferably substantially greater than the motion along lateralaxis 40. Substantially greater refers to a difference by a factor of atleast 3, and preferably a factor of 10.

A driven element 42 is placed in contact with a selected contact portion44 of the vibration element 26. As illustrated in FIGS. 1–2, theselected contact portion 44 comprises an edge of the vibrating element,although other locations could be used. As used herein, unless otherwiseindicated, the term “edge” should be construed to include a corner wheremultiple surfaces converge, as for example, in the corner of arectangular cross-sectional rod where three planar surfaces converge(and where three edges converge). Moreover, other shapes of contactingsurfaces could be used other than an edge. For example, a beveledsurface inclined at an angle selected to place contacting surface 44into flat engagement with the engaging surface of driven element 42could be used. Given the present disclosure, many configurations can bederived to ensure that the engaging surface 44 provides the neededengagement to move the driven element 42.

As illustrated, the driven element 42 comprises a rod with a cylindricalcross-section, although other shapes of driven elements can be used. Thecenter line 25 of the vibration element 26 and a centerline 45 of rod 42are in the same plane, and separated by an angle α of about 30 degreesas measured in that plane. The orientations of the centerlines 25, 45and the angle α will vary with the particular application. The angle αis difficult to analytically determine, and is preferably adjustedaccording to the motor design. Typically it is between 10 and 80degrees, and preferably between 20 and 60 degrees. The driven element 42is supported so it can move along the longitudinal axis 45 of the drivenelement 42. The driven member is supported so that it can move relativeto the vibration element 26, which is effectively held stationary in theillustrated embodiment. The driven element 42 translates along the axis45, as explained in greater detail below.

As illustrated, the support of the driven element 42 can be achieved bywheels 46, which provide a low resistance to motion along the axis 45.This support is achieved here by placing an inclined surface on thewheels 46, which abut the curved sides of rod-like driven element 42 androtate as the rod translates along axis 45. The wheels are located onthe side of the driven element 42 opposite the selected contact portion44, with the contact portion 44 also being further located between twowheels 46 in a direction along the axis 45, so that the wheels 46 andselected contact portion 44 restrain motion of the driven element 42 inall directions except along axis 45. The wheel 46 could also contact thedriven element 42 using a flat edge of the wheel concentric with therotational axis 65, as illustrated in FIG. 74. The wheels 46 could alsohave contoured peripheries configured to engage mating shapes onadjacent portions of the driven element 42 in order to appropriatelysupport and guide the driven element 42. Given the present disclosure, avariety of movable support configurations will be apparent to thoseskilled in the art.

The vibration element 26 is advantageously resiliently urged against thedriven element 42, and FIGS. 1–2 show one of many ways to achieve this.The elliptical motion 100 of the selected contacting portion 44 ispreferably an unrestrained motion, one that occurs whether or not thecontacting portion 44 engages a driven element, and one that is achievedwithout relying on any resistance from being urged against the drivenelement 42. Nevertheless, the selected contacting portion 44 isadvantageously resiliently urged against the driven element 42 in orderto enhance the driving engagement of the driving and driven parts.

A spring 50 made of flat, elongated spring material is bent into an “L”shape with opposing ends 50 a, 50 b. A first end 50 a of the spring isfastened to a base 52. A second end 50 b of the spring is fastened tothe end of the vibration element 26 through which the screw 32 extends,with a hole in the end 50 b of spring 50 allowing passage of the screw.A first leg of the spring 50 which contains end 50 a is generallyparallel to the longitudinal axis of vibration element 26, and thesecond leg of the spring 50 that contains the end 50 b is generallyparallel to the axis 38, with the two legs being generally perpendicularto each other. The spring 50 resiliently urges the vibration element 26against the driven element 42 at the selected contact portion 44.Variations in the location of the mounting at end 50 a, 50 b can be usedto vary the pre-load with which the vibration element 26 is urgedagainst the driven element 42. As discussed later, variations in theshape, cross-section, location, and form of the resilient element 50 arepossible and can be used to achieve a desired vibration mode.

The spring 50 is designed to optimize the vibration characteristics ofvibration element 26 as well as provide a sufficient range offlexibility to insure contact between the driven element 42 andvibration element 26. This contact and a defined range of contactpressure should be maintained throughout the life of the motor assembly20. The spring 50 advantageously compensates for manufacturingtolerances and uncertainties and also can compensate for wear that mightreduce the size of the vibration element 26 at the selected contactportion 44.

As discussed further below, during operation the vibration element 26might touch the driven element 42 only part of the time due to thevibration and in such a case the spring 50 preferably is designed toensure suitable engagement. The spring constant and the location of thespring can be used to adjust the percentage of contact and non-contacttime. This allows a designer the ability to configure the motor assembly20 to ensure the resulting engagement between engaging portion 44 anddriven element 42 is with sufficient force to move the driven element 42with sufficient force to achieve the desired objectives of motorassembly 20. Moreover, variations in the dimensions affecting theengagement of the selected engaging portion 44 and the driven element 42will be accommodated by the mounting system, such as spring 50, thatresiliently urges the contacting parts into engagement. This flexibilityin manufacturing tolerances allows a reduction in manufacturing costsand in alignment tolerances and costs.

In the depicted embodiment the wheels 46 are both rotatably mounted toaxles connected to the base 52. Other schemes of mounting the drivenelement 42 are possible given the present disclosure. For example, thebase 52 could support one or more projections having aligned holes intowhich linear bearings are preferably placed, with the elongated drivenmember 42 extending through the holes. This configuration would allow anelongated driven member 42 to translate along an axis, but wouldrestrain other motions. The motor can be as small as 25×25×5 mm³ or evensmaller.

Operation:

Referring primarily to FIGS. 1–2, when an electrical signal of suitablefrequency, waveform and voltage is applied to the piezoelectric element22 the vibration element 26 starts to move the rod 42. For theembodiment shown, preferred waveforms are sine waves or rectangularlyshaped waves. The direction of the linear motion generated is determinedby the frequency. A motor assembly 20 operating, for example, at about35 kHz in one direction and at about 60 kHz in the other direction isbelieved to be suitable for a variety of potential uses. Other frequencypairings are possible and will vary with a variety of factors concerningthe design of motor assembly 20. The operating frequencies can bechanged by changing the design of the various components, with theoperating frequencies being selected to be inaudible by humans and bymost pets in some preferred embodiments. The operating voltage will varywith the type of piezoelectric 22 or other vibration source used. Amulti-layered piezoelectric 22 operating at 6 volts peak-to-peakamplitude is believed useful for a variety of applications.

The vibration of the piezoelectric element 22 makes the vibrationelement 26 vibrate in a way so that the selected contact portion 44performs an elliptic motion relative to the driven element 42. Asdiscussed below, the vibration of the piezoelectric 22 excited at afirst frequency makes the vibration element 26 vibrate in a way so thatthe selected contact portion 44 performs a first elliptic motion 100 arelative to the driven element 42. The elliptical motion is achieved byhaving the first signal excite two resonant modes of the resonator 24,resulting in the desired elliptical motion 100 a—preferably withoutrequiring engagement with the driven element 42 to achieve thiselliptical motion. That first elliptical motion 100 a moves the drivenelement 42 to the right as depicted in FIG. 1.

Moreover, vibration of the piezoelectric 22 excited at a secondfrequency makes the vibration element 26 vibrate in a way so that theselected contact portion 44 performs a second elliptic motion 100 brelative to the driven element 42 in a different direction andorientation than that of elliptical motion 100 a, and preferably, butoptionally, in a direction opposite that of elliptical motion 100 a. Asdepicted, the second elliptical motion is clockwise and that will movethe driven element 42 in an opposite direction, to the left as depictedin FIG. 1. Typically, the elliptical motions 100 a, 100 b do notoverlap, but have different major and minor axes, amplitudes andorientations. Ideally, the elliptical motions 100 a, 100 b overlap. Theelliptical motions 100 a, 100 b are preferably achieved withoutrequiring that the selected contact portion 44 engage the driven element42.

This results in the selected contacting portion 44 moving the drivenelement 42 in a first direction when the source of vibration is drivenby the first signal, and moving the driven element in a second directionwhen the source of vibration is driven by the second signal. Butadvantageously the selected contacting portion further moves in thefirst direction when a single sinusoidal signal of a first frequency isapplied. Moreover, the selected contacting portion 44 can also move inthe first direction when the first frequency is dominant andsuperimposed with plural sinusoidal signals of different frequencies. Inthis later instance, the second signal either does not occursimultaneously with the first signal or it is of substantially differentamplitude if it occurs simultaneously with the first signal. Bydifferent in signal amplitudes a factor of about 10 is consideredsubstantially different, and preferably the amplitudes differ by afactor of 100 or more. The result is that the elliptical motion 100 canbe achieved by a simple sinusoidal signal. Alternatively, it can beachieved by complex signals of different frequencies—for example, thecomplex frequencies that are superimposed to generate sawtooth waves.

During driving engagement of the selected contacting portion 44 with thedriven element 42, it is believed that the elliptical motion 100consists of a phase where the vibration element 26 is pressed againstthe driven element 42 and a phase where this is not the case. The motioncomponent of the vibration element that has the direction along thelongitudinal axis 45 of the driven element is partly transferred to thedriven element by the friction between the vibration element 26 and thedriven element 42. In the second phase the vibration element 26 moves inthe opposite direction. In this second phase the vibration element doesnot transfer any motion component parallel to the axis 45 because thevibration element 26 is not pressed against the driven element.

In contrast to other vibrating motor designs, the required manufacturingtolerances are believed to be significantly looser so that no precisemanufacturing is needed to alternate between the contact and no contactsituations. The necessary equilibrium is created by the design,specifically including spring and the mass of the vibration element 26.

Because the high frequencies (over 30 kHz) and small motions make itdifficult to actually determine the contact, it is also believedpossible that there is always contact between the vibration element 26and the driven element 42. In that situation, the motion of the drivenelement 42 is believed to be caused by the difference in force at theselected contact portion 44 caused by the elliptical motion of thecontact portion 44 which provides a resultant force in only onedirection, or primarily in only one direction, thus driving the drivenelement 42 in that direction. Further discussions of this ellipticalmotion and a number of design aspects are discussed below.

Whatever the actual mechanism, the driven element performs a linearmotion with the direction of the motion being determined by the motionof the selected contact portion 44 of the vibration element 26. If thecontact portion does a counterclockwise elliptical motion, the drivenelement 42 will move to the right as depicted in FIG. 1. If the motionis clockwise, it will move in opposite direction.

It is possible that the vibration element 26 will also be excited tomove along axis 40, which could result in rotation of the cylindricalrod-like driven element 42. Depending on the relative magnitudes of themotion of the selected contact portion 44 and depending on itsorientation and contact with the driven element 42, and if the bearingsupports are properly configured, both translation and rotation couldsimultaneously occur.

Further, referring to FIG. 2, it is believed possible to select the axiswith the largest motion to be longitudinal axis 25, but to select thelateral axis 40 as having the next largest and only other significantmotion. In that instance the motor assembly 20 would cause a rotation ofthe rod-like driven element 42 about longitudinal axis 45. To providethis rotational motion, the selected contact portion 44 would have toprovide an elliptic motion having a substantial portion of its motion ina plane generally orthogonal to the axis 45 of the driven element 42 inorder to impart rotational motion to the driven element. The directionof rotation would again depend on the direction in which the selectedcontact portion 44 performs the shape of the ellipse.

Moreover, it is believed possible to select the axes with the largesttwo motions, and only significant motions, to be the lateral axes 38,40, which could again result in an elliptical motion of the selectedcontact portion 44 in a manner that engages the driven element 42 torotate it about longitudinal axis 45 during one portion of movement andto disengage sufficiently to prevent motion or noticeable detrimentalmotion in the other portion of movement of the selected contact portion44.

An alternative embodiment is shown in FIG. 4, where instead of anelongated driven element 42 a rotatable wheel 60 is mounted to be drivenby the vibratory element 26 having a portion placed in contact with anappropriately located driven surface 62 on the wheel 60. In thisembodiment the wheel 60 is mounted to rotate about rotational axis 65 ona bearing. The driven surface 62 is preferably placed on a side 64 ofthe wheel located in a plane orthogonal to the rotational axis 65 aswith driven surface 62 a, or placed along a surface concentric 62 b withthe axis 65. The wheel 60 could comprise a variety of elements,including a gear. The selected contact portion 44 of the vibratoryelement 26 engages the driven surface 62 to cause movement of the wheel60 about the rotational axis. The wheel 60 will rotate in the oppositedirection of the motion of the contact point around the elliptical pathtraveled by the contact portion 44. Thus, if the contacting portion 44of the vibration element 26 moves clockwise the wheel 60 will movecounterclockwise, so that the contact portion on the wheel and on thevibration element share the same motion while they are in contact.

FIG. 5 shows a further embodiment. The motor assembly 20 has a vibrationelement 26 that contains a resonator 24 in the shape of a C-clamp 74.The piezoelectric element 22 is held in the clamp. To transmit themotions, a first electrical signal causes the piezoelectric element 22to move in the vibration element 26 which causes the contacting portion44 to move in a first an elliptical motion 100 a.

The piezoelectric element 22 is clamped by the screw 32 which extendsthrough leg 73 and presses against insert plate 34 to compress thepiezoelectric element 22 between the plate 34 and an opposing leg 75 ofthe C-clamp resonator 74. This clamping causes pre-load in thepiezoelectric element 22, which increases and preferably optimizes thelifetime and performance of the piezoelectric element 22.

The legs 73, 75 of the C-clamp between which the piezoelectric element22 is held, could be of similar stiffness, but are advantageously ofdifferent stiffness. Advantageously one leg 73 is at least a factor of10 times stiffer than the opposing leg 73. The more flexible leg 75vibrates with larger amplitude than the stiffer leg 73. The selectedcontacting portion 44 is preferably located on the less stiff leg 73 inorder to achieve a larger amplitude of motion at the selected contactingportion 44. Moreover, in this configuration the leg 73 is placed inbending stress, with the largest stress being adjacent the interior endof the leg. A notch 77 can be placed adjacent to that location in orderto localize the bending so that the leg 75 pivots about the notch 77.

A spring element 50 has a first end 50 a connected to the base 52 and asecond end 52 b connected to a vibration element 26 to keep thevibration element in contact with the driven element 42. The second end50 b is shown as connected to the head of the screw 32 although otherconnections to the resonator 74 could be used. In this embodiment thespring 50 is depicted as a tension coil spring. The resonator 74 isloosely pinned by pin 78 extending through hole 80 and into the base 52so the resonator 74 can pivot about pin 78. The pin 78 is offset fromthe line of action of spring 50 so that the contacting portion 44 isresiliently urged against driven element 42.

The spring 50 is under tension in the depicted configuration. The spring50 provides a sufficient range of flexibility to ensure contact betweenthe driven element 42 and the vibration element 74. This contact and adefined range of contact pressures are advantageously maintainedthroughout the life of the motor assembly 20. The spring 50advantageously is designed to compensate for manufacturing uncertaintiesand wear that might reduce the size of the vibration element 26 at theselected contact portion 44.

To prevent the driven element 42 from separating from the vibrationelement 26, wheels 46 connected to the base 52 are provided aspreviously discussed. Alternatively, the base 52 can be equipped withsidewalls 80 having holes through which the driven element 42 extends inorder to support the driven element while allowing it to move along itsdesired translational axis. Advantageously, the holes in the sidewalls80 are designed to reduce friction, and thus could have linear bearingssupporting the driven element 42. If the holes in the sidewalls 80 areenlarged so that they do not permanently contact the driven element 42,they function as auxiliary bearings instead and protect the drivenelement 42 from being forcefully pushed into the vibration element 26 byexternal forces, which could be damaging to the vibration element 26 aswell as its suspension.

When an electrical signal of suitable frequency, waveform and voltage isapplied to the piezoelectric element 22 the vibration element 46 startsto move the driven element 42. The direction of the linear motiongenerated is determined by the frequency. Changing the configuration ofvarious components of the motor assembly 20, as discussed further below,can change the operating frequencies. In the depicted example, amulti-layered piezoelectric element is used that could operate the motorassembly 20 on 6V peak-to-peak amplitude to drive a cylindrical rod 44.

The vibration of the piezoelectric 22 at a first frequency makes thevibration element 26 vibrate in a way so that the selected contactportion 44 performs a first elliptic motion relative to the drivenelement 42. The elliptical motion consists of a phase where thevibration element 26 is pressed against the driven element 42 and aphase where this is not the case, as discussed in further detail below.If the selected contact portion 44 moves in a counterclockwiseelliptical path 100 a as depicted, the driven element 42 will move tothe right as depicted in FIG. 5.

Advantageously, the vibration of the piezoelectric 22 excited at asecond frequency makes the vibration element 26 vibrate in a way so thatthe selected contact portion 44 performs a second elliptic motion 100 brelative to the driven element 42 in a direction opposite that ofelliptical motion 100 a. As depicted, the second elliptical motion isclockwise and that will move the driven element 42 in an oppositedirection, to the left as depicted in FIG. 5. Typically, the ellipticalmotion 100 a, 100 b do not overlap, but have different major and minoraxes, amplitudes and orientations. Ideally, the elliptical motions 100a, 100 b overlap. The vibrating element 26 could be configured to causethe second elliptical motion 100 b to be in a different orientation, asfor example, to rotate a driven element 42.

In more detail, vibration of the piezoelectric element 22 causes thevibration element 26 to begin oscillating about the pin 78, which causesthe contact portion 44 to have an up-and-down motion and a back-andforth motion along its elliptical path 100. The up-down motion and theback-forth motion are out of phase, and the contact portion 44 thus hasan elliptical motion along one of paths 100 a, 100 b. That causes therod-like driven element 42 to begin motion. The rotation of thevibration element 26 can be caused by interaction of the contactingportion 44 with the driven element 42, which may be viewed as conservingangular momentum about the pin.

The vibratory motor 26 of FIG. 5 could be used with a rotating drivenelement 42 as depicted in FIG. 4, and could be used in other drivingarrangements.

FIG. 6 shows a further embodiment in which the vibrating element 26 ismounted in a stationary manner, and the driven element 42 is resilientlyurged against the vibrating element. If the driven element 42 iselongated, and especially if it comprises a rod or other structure thatis flexible, merely pressing the driven element against the vibratingmotor 26 may cause the parts to resiliently urged into contact. Thatrequires the support of the driven element 42 to be such that aresilient support is inherently provided by the flexibility of thedriven element. If that is not the case, a resilient support must beprovided for the driven element 42, or a resilient support can beprovided in addition to the flexibility of the driven element. Such aresilient support is illustrated schematically by springs 50 a, 50 b,resiliently urged against the selected contacting portion 44 a, 44 b ofthe vibrating element 26.

In this embodiment, the vibration element 26 is configured with aspecial shape so that there are more than one, and preferably a numberof selected contacting portions 44 a, 44 b, . . . 44 n. The ability touse different portions of the vibrating element 26 to generate a desiredelliptical motion 100 resulting from free vibration modes excited at aspecified frequency, offers the ability to have a variety ofarrangements. For each of several separate excitation frequencies, adifferent selected contacting portion 44 can resonate in a predeterminedelliptical motion 100. Alternatively, the same selected contactingportion 44 may resonate at a different excitation frequency to cause anelliptical motion but in a different orientation. Preferably theelliptical motion is in opposite direction to reverse the motion of thedriven element, but other motions are possible depending on the needs ofthe user. As a result, several driven elements 42 a through 42 n thatare resiliently urged against separate and corresponding selectedcontacting portions 44 a through 42 n, can be individually controlled.

For example, it is believed possible to have one driven element 42 atranslate, and another driven element 42 b rotate, by generatingappropriately orientated elliptical paths 100 a, 100 b respectively, atselected contacting portions 44 a, 44 b, respectively. The generation ofthe elliptical paths 100 a, 100 b is preferably caused by a singleexcitation frequency to piezoelectric element 22, which causes asufficiently resonant vibration to generate the elliptical paths.Alternatively, a first excitation frequency could be required togenerate depicted motion 100 a, and a second excitation frequency usedto generate motion 100 b. Yet other excitation frequencies provided bythe piezoelectric 22 could be used to change the direction of theelliptical motion to travel in an opposing direction.

Moreover, while the contacting portions 44 a, 44 b are shown at thedistal ends 36 of the vibrating element 26, the contacting portions 44could be at various locations and orientations on the vibrating element26. This is shown illustratively by engaging portion 44 n and drivenelement 42 n, with the driven element 42 n rotating (e.g., to drive agear) or translating along its longitudinal axis.

These aspects are further illustrated by the embodiment of FIG. 62,which shows that the selected contacting portion 44 need not occur atthe distal end 36 of the vibratory element 26. In FIG. 62 the vibratoryelement 26 has one or more selected contacting portions 44 e locatedalong the periphery of the element along the longitudinal length of theelement. A second one or more selected contacting portions 44 f arelocated on an opposing surface of the vibratory element. Preferably theselected contacting portions 44 comprise slightly raised areas extendingabove the surrounding portion of the vibratory element 26. A drivenelement 42 such as a cylindrical shaft is placed in contact with thecontacting portions 44 e. In the depicted embodiment, the axes 25, 45 ofthe vibratory element 26 and driven element 42 are aligned and coplanar,but that need not be the case.

When the vibratory element 26 is excited at a first frequency, thecontacting portions vibrate in an elliptical path 100 a causing motionof the driven element 42 in a first direction. The contacting portion 44e moves in an elliptical path opposite to that of contacting portion 44f. To shift the motion of the driven element 42, the contacting portion44 f and driven element 42 are placed into contact. This can be achievedby moving one or both of the vibrating element 26 and driven element 42.A rotation of the vibratory element 26 would suffice in the illustratedembodiment. Thus, a single excitation frequency could result in opposingdirections of movement of the driven element 42. This embodiment alsoshows that the contact between the vibration element 26 and the drivenelement 42 can be a multiple point contact. It is not limited to asingle point contact. This also allows, for example, the use of only onebearing pressing a driven rod 42 at two to four points against thevibration element 26. The increased number of contacting portions 44 canincrease the frictional engagement with the driven element 42 and allowa greater power to be exerted on the driven element 42, and thus allow agreater power to be exerted by the driven element 42.

Alternatively, more than one driven element 42 could be placed incontact with differing portions 44 of the vibratory element 26,achieving different motions for each driven object. Moreover, thevibratory element 26 could be urged against a stationary surface and byselecting various contacting portions 44 (e.g., 44 e, or 44 f), move thevibratory element and any object connected to the vibratory element invarious directions over the surface.

Preloaded Motor Configurations

It is advantageous in many cases to use multilayer piezoelectricelements 22. These elements 22 are preferably of rectangularcross-sectional shape, but other shapes could be use such as square,circular, or other shapes. The piezoelectric elements 22 have layers ofpiezoelectric material with printed electrodes that are stacked on topof each other. Often many piezoelectric components are made at the sametime by producing a large stacked plate that is pressed and cut to formmany single piezoelectric elements.

As a result of this manufacturing method, the mechanical output areas ofthe piezoelectric are typically parallel to the electrode layers and arealso flat. In order to use multilayer piezoelectric elements, amechanical preload is often applied. This increases the lifetime of thepiezoelectric by preventing delamination under dynamic movement of thepiezoelectric element, and it also optimizes the contact between thepiezoelectric element 22 and the resonator 24 in which it is mounted. Asa result, mechanical motion generated by the piezoelectric element 22 isefficiently transferred through the contact zone to the resonator.

There are different methods to generate the preload. A resonator 24 canbe used that has two parts. A spring is used to generate the preload byinserting a piezoelectric element 22 and the compressed spring betweenthe two parts of the resonator which are then welded or otherwisefastened together. This way, a permanent preload is generated.

An alternative way to generate the preload is shown in FIG. 1, where thepreload is preferably achieved by having the resonator 24 exert apressure on the piezoelectric element 22. The compression ensures thatthe vibrations of the piezoelectric element 22 are transferred to theresonator 26 and selected contacting portion 44. The compression alsoavoids at least some damage to the piezoelectric element 22 when highvoltages are applied. The pressure is equal to the axial force on thepiezoelectric element 22 divided by the area over which the force acts.This area is the contact area between the piezoelectric element 22 andthe abutting portions of the resonator 26. Because the contact area canbe difficult to measure, it is more straightforward to use the forcerather than the pressure as a characterizing parameter.

The force exerted on the piezoelectric element 22 when no current ispassed through the piezoelectric element 22 includes: a static pre-loadequal to the axial force in the sidewalls 29 counteracting the preloadand a load component from the contact force arising from the contactsurface 44 being urged against the driven object 42. All of these forcesfluctuate when a fluctuating current is passed through the piezoelectricelement 22.

The piezoelectric element 22 can be aligned so that the preload on thepiezoelectric element 22 is in the most active direction of thepiezoelectric element 22. While this is not necessary for the vibratorymotor 26 to operate, this configuration results in the highestefficiency. Preferably, for the beam-type vibratory element 26 depictedin FIG. 1, the greatest motion occurs in the line 3—3 direction that ispreferably aligned with the longitudinal axis 25.

Methods of producing a preload on the piezoelectric element 22 that aredescribed herein include: (1) clamping the piezoelectric element 22 inthe resonator 24 with a threaded fastener or other compressivemechanism; (2) using force to press the piezoelectric element 22 into ahole in the motor body in a manner similar to press fitting of shafts;and (3) combinations thereof. Other preload mechanisms can be used. Thefollowing disclosure expands on the threaded fasteners described thusfar, and then discusses some press-fit mechanisms and methods. Awedge-based method and some variations on the above methods conclude thediscussion.

Threaded Preload Device & Method: FIGS. 1 and 5 illustrate a threadedfastener preload method and apparatus that is further described below.The resonator element 26 is configured so that a hole, cavity or opening28 is formed to accommodate the piezoelectric element 22. The resonatorcan have various shapes, for example cross-sections that are round,square, rectangular, or polyhedral. The opening 28 is larger than thepiezoelectric element 22 in all dimensions. A threaded fastener 32extends through a hole in a stationary object in order to allow thedistal end of the fastener 32 to press the piezoelectric element 22against the resonator 24. The threaded fastener 32 advantageously passesthrough a threaded hole in the resonator to directly abut the plate 34that is urged against the piezoelectric element 22.

Once the parts are assembled, a preload can be achieved in thepiezoelectric element 22 by tightening the threaded fastener 32. Thepreload can be approximately calculated by tightening the fastener 32 toa known torque. The threaded fastener 32 need not be aligned with thelongitudinal axis of the piezoelectric 22, but can be offset in avariety of ways so that tightening the threaded fastener urges twobodies toward each other to compress the piezoelectric element 22. Avariety of other mechanisms can be used to place the piezoelectricelement 22 in compression. Other preloading mechanisms are discussedlater.

Uni-Axially-Stressed, Press-Fit Preload Device & Method: Several aspectsof the press-fit of the piezoelectric element 22 are described withrespect to FIG. 7 a. The resonator 24 is configured so that a hole oropening 28 for the piezoelectric element 22 is formed in the resonator,with sidewalls 29 defining the sides of the opening. The opening 28 isslightly smaller in the axial direction of the piezoelectric element 22than the combined length of the piezoelectric element 22 and any otherelements to be pressed into the opening 28. The required interferencebetween the resonator 24 and the parts to be pressed into the opening 28depends on the geometry and dimensions of all parts and also the elasticstrain of the material from which the resonator 24 is made.

Referring to FIG. 7 b, the piezoelectric element 22 can be presseddirectly into the resonator 24.

This press-fit can be made easier by providing a tapered surface 82which places an inclined contact area between the abutting edges of atleast one of the piezoelectric element 22 and an end wall of theresonator 24 at the mating portion of opening 28. The inclined surface82 avoids an offset, abutting-type of interference, and provides asliding interference at the start of the press-fit. An improved way toachieve this press-fit is described later. This preload mechanism andmethod produces large shear stresses on the contacting surfaces of thepiezoelectric element 22. Because the piezoelectric material is brittle,the stresses can result in cracking of the piezoelectric element 22. Toavoid these shear stresses and protect the piezoelectric element 22, itis also possible to simultaneously press in a piezoelectric element 22sandwiched between two strips of a less brittle material 84 (FIG. 7 a)such as a metal, preferably steel. The strips of material 84 can have avariety of shapes suitable to the configuration of the piezoelectricelement 22 and the vibrational element 26. The protective cap 84 canalso advantageously be used to guide the piezoelectric element 22 intothe opening 28, thereby eliminating the need for tapering of any parts.One of the strips of material 84 can advantageously comprise the end 50b of spring 50 that connects the vibrating element 26 to the base 52.

When the piezoelectric element 22 and any end protectors 84 are insertedinto the opening 28, the sidewalls 29 are stretched to accommodate thelonger length element 22 and any end protectors 84. The stretchedsidewalls 29 act as springs and maintain the preload on thepiezoelectric element 22. Ideally, the preload on the piezoelectricelement 22 could be specified by knowing the cross-sectional dimensionsof the sidewalls 29 and fixing an interference that results in anelastic strain in the sidewalls 29 and therefore known stress andpreloads in the sidewalls. The preload is then this stress multiplied bythe combined cross-sectional area of the sidewalls 29.

Unfortunately, this method may not be practical because the requiredinterference for small vibratory elements 26 of an inch or less inlength is likely to be too small, on the order of 0.0001 inches, whichis beyond a tolerance currently obtainable by traditional machiningprocesses at a reasonable cost. Larger vibratory elements may havelarger preloads that require larger dimensions, but the accuracy neededto achieve those dimensions is likely to require similarly smalltolerances and thus also require expensive machining or polishing. Thisarises in part because small variances in the interference would resultin great differences in the preload when the sidewalls 29 are in theelastic portion of the stress-strain curve and act as a spring as thepiezoelectric element 22 expands and contracts.

Because of these disadvantages, it is desirable to make the interferencebetween the length of the vibratory element 26 and the opening 28sufficiently large so that the sidewalls 29 forming the opening 28 arestressed beyond their yield strength but below their ultimate tensilestrength, and a sufficient amount below their fatigue strength toprovide an acceptable product life. When stressed beyond the yieldstrength, the sidewalls 29 provide a relatively constant preload eventhough the dimensions of the opening 28, or the piezoelectric element 22or the end protectors 84 may vary. This allows looser manufacturingtolerances and results in greatly simplified manufacturing andsignificantly lower costs.

The plastic portion of the stress-strain curve from yield up to thepoint where necking of the sidewalls 29 begins, can be used to achievethe desired preload. The usable portion of the strain occurring afteryield and before necking is at least ten times larger than the elasticportion in strain. This is believed to apply to all non-ferrous metals,which are the preferred material for the resonator 24, with aluminumbeing the most preferred non-ferrous metal. Ferrous metals and somenon-metallic materials could also be used in other embodiments.

This method significantly loosens the required tolerance on theinterference fit between the vibratory element 26 and the opening 28.Further, the slope of the stress-strain curve above yield is much lessthan that of the elastic portion. Thus, the preload will also not dependso greatly on the amount of interference. Using this method and design,the preload can be estimated as the yield strength multiplied by thecombined cross-sectional area of the sidewalls 29 for the depictedconfiguration. Other configurations will require other calculations, butsuch calculations are known to one skilled in the art and are thus notdescribed in detail herein.

The press-fit method has several advantages over using threadedfasteners to preload the piezoelectric element 22. The performance ofpress-fit piezoelectric elements 22 is more repeatable because thepreload and contact area are better defined. Furthermore, the preload ofa press-fit piezoelectric elements 22 can be easily calculated and doesnot depend heavily on manufacturing tolerances. The press-fit methodalso reduces the number of total motor parts, because it does notrequire the spring 50 to be clamped separately to the vibrating element50 as the end 50 b can be used to press-fit the piezoelectric elements22 into the opening 28. In addition, assembly of the vibratory element26 is made easier by eliminating the need for a threaded fastener 32 anduncertainties in its tightening and loosening during vibration.Eliminating the threaded fastener 32 also eliminates the need for atapped hole and thus reduces manufacturing costs.

The vibratory element 26 shown in FIG. 1 has two straight sidewalls 29on opposing sides of the opening 28. The sidewalls could comprisedifferent configurations, such as beams at each corner. But in theseconfigurations the sidewalls 29 are straight and generally parallel tothe longitudinal axis of the piezoelectric element 22. That results insidewalls that remain primarily in uni-axial tension during preloadingand operation of the piezoelectric element 22.

Curved-Beam Configurations for Press-Fit Preloads: Alternativeconfigurations having sidewalls that curve away from the piezoelectricelement and from each other can provide a number of advantages. Thepress-fit operation for these two general types of vibratory elements 26does not differ. But the resulting advantages of the basic configurationcan differ significantly, as discussed below. The source of the problemand some partial solutions are discussed first, and then the advantagesof curved sidewalls 29 are discussed relative to FIG. 8.

Referring to FIG. 7, the preload on the piezoelectric element 22 isestimated as the yield strength of the material multiplied by thecombined cross-sectional area of the sidewalls 29, because the sidewallsare stressed in uniaxial tension. This means that the entirecross-section of a sidewall 29 experiences the same stress. If thesidewalls 29 have the same cross-sectional area and the piezoelectricelement 22 is pressed so its longitudinal axis coincides with thelongitudinal axis 25 of the vibratory element 26, then the sidewalls 29also experience the same force and the same stress. If the sidewalls 29are of constant cross-sectional area, the stress is also constant overthe length of the sidewalls measured along the longitudinal axis 25 ofthe vibratory element.

The piezoelectric element 22 must move the resonator 24 and selecteddriving portion 44 to achieve a sufficient physical displacement to movethe driven element 42. Because the sidewalls 29 act as springs topreload the piezoelectric element 22, a portion of the preload must beovercome in order to extend the vibratory element 26 and move theselected contacting portion. If the stiffness of the sidewalls 29 is toolarge, too much of the energy of the piezoelectric element 22 may beexpended in pushing against the sidewalls 29 and the amount of vibratoryenergy that is transferred to movement of the selected contactingportion 44 and driven element 42 thus is reduced.

For a small vibratory element 26 of about one inch (2.54 cm) or less inlength, the maximum forces on the piezoelectric element 22 and thedesire to have the sidewalls 29 in the yield region result inconfiguring the sidewalls 29 to have a thickness on the order of 0.01inches (0.25 mm). At such dimensions, or smaller, inaccuracies inmanufacturing parts of aluminum can result in significant percentagedifferences in the thickness of sidewalls 29. This leads to largerstresses in areas with smaller cross-sections and ultimately aconcentration of stresses and strains in the smallest cross-sectionalarea. This concentration of stresses and strains over a short section ofthe sidewall 29 increases the chance of necking in this region duringthe press-fit operation.

Necking is undesirable for several reasons. Because all further strainin the sidewalls 29 produced by handling, temperature changes, oroperation of the motor assembly 20 will be concentrated in the veryshort necked region, the large stresses and strains in the necked regioncan lead to fatigue failure during operation of the motor assembly 20.Moreover, the necking can result in the geometry and therefore thevibrations of the sidewall 29 and vibratory element 26 to change andalter the performance of the motor assembly 20.

Fatigue failure in vibratory elements 24 with sidewalls 29 inpredominantly uniaxial tension is a concern even when necking is notpresent. Because the sidewalls 29 are put into yield, the fatigue meanstress during motor operation is near the yield strength of thematerial. The amplitude of the stress is very small because thepiezoelectric element 22 produces deflections on the order of hundredsof nanometers as it operates at about 30 kHz–90 kHz. The highfrequencies result in very large cycles of operation, but at very smallamplitudes. Ferrous metals have a stress endurance limit such that thesemetals, if operated below this limit, do not suffer from fatiguefailure. An endurance limit for aluminum and other nonferrous metals hasnot been observed (at least not below 100 million cycles). There is aconcern that small stress amplitudes eventually may lead to fatiguefailure in these materials because the motors 20 are operated atfrequencies in the range of tens of kilohertz, and at this rate it doesnot take more than several hours for a motor to accumulate more than abillion stress amplitude cycles, albeit cycles of low amplitude.

Published fatigue data here is not available but fatigue failures insuch motors have been observed at more than one billion cycles implyingthat it is desirable to take steps against fatigue failure. Using amanufacturing process that produces sidewalls 29 with nearly constantcross-sectional dimensions will improve fatigue properties by allowingthe entire sidewall 29 to absorb stresses and strains instead of justone small area of the sidewall. Improving the surface finish of thesidewalls 29 also helps by reducing the number of crack initiationsites. Assuring that the sidewalls are equally stressed by giving themthe same cross-sectional area and taking care to center thepiezoelectric element 22 will also help avoid fatigue failure.

Referring now to FIG. 8, a vibratory element 26 p is shown that can beused with any of the motor assemblies 20 described herein. The vibratoryelement 26 p has curved sidewalls 29 p, which are put in a morecomplicated state of stress, when the piezoelectric element 22 ispressed into opening 28 p in resonator 26 p. The opening 28 p hasopposing flat portions 31 to abut the ends of the piezoelectric element22, and is configured to produce curved sidewalls 29 p. Thus the opening28 p is generally circular but with two opposing flats locatedorthogonal to an axis 25 p corresponding to the longitudinal axis of thepiezoelectric element 22. The remainder of the resonator 24 p can havevarious configurations suitable to the desired motion of and location ofthe selected contacting portion 44. Here the resonator 24 p is shownwith a rectangular configuration except for the opening 28 p defined bycurved sidewalls 29 p. The curved sidewalls advantageously have auniform cross section along the curved length, with the depictedconfiguration having a rectangular cross-section along the length of thecurved sidewalls. The curved sidewalls preferably have a uniform crosssection for a substantial portion of the length of the sidewall. As usedhere, that substantial length advantageously refers to more than halfthe length of the sidewall 29, and preferably refers to 75% of thelength of the sidewall 29, and ideally refers to over 90% of the lengthof the sidewall 29 between the end walls 31.

For curved sidewalls 29 p, the stress state can still be approximated asuniaxial but the stress in the sidewalls is not uniform and is actuallya combination of bending and axial stresses. These stresses can bedetermined using classical beam theory calculations. Alternatively, thedeformations of the sidewalls can be approximated by finite elementmethods or Castigliano's theorem.

In this embodiment, the sidewalls 29 are also advantageously put intoplastic deformation during the press-fit of the piezoelectric element 22and any protective plates 84 in order to make the preload approximatelyconstant regardless of small differences in the amount of theinterference fit. But the vibratory element 26 p has sidewalls 29 p thatare not uniformly stressed, and are instead stressed like a curved beamin bending. The curved configuration of the sidewalls 29 p alwaysresults in the maximum stress being located on the outside and insidesurfaces of the sidewalls 29 p, at the ends of the curved walls 29 pjoining the main body of the resonator 24. These stresses basicallyoccur where the curved walls 29 p join the remainder of the body of theresonator 24. These stresses occur on the inside of the walls 29 pforming the opening 28 p, and also on the outside of the walls 29 p. Thecurved walls result in four defined areas of maximum stress 86 on eachsidewall 29 p, two on the inside of the walls and two on the outside ofthe walls.

Significantly, this implies that these areas reach plastic deformationfirst rather than having the entire cross-section of sidewall 29 reachplastic deformation simultaneously when the piezoelectric element 22 ispress-fit into the opening 28 p. This localized yielding can haveadvantageous results.

The vibratory element 26 p has several advantages over the vibratoryelement 26 of FIG. 7 a. Because the sidewalls 29 p are curved, they canbe much thicker than straight sidewalls 29 and still achieve the samepreload on the piezoelectric element 22. This is better formanufacturing and better for the fatigue lifetime of the vibratoryelement 26 p. Thicker walls increase the fatigue lifetime because smallmaterial flaws and manufacturing errors will be proportionally smaller.Such material flaws and manufacturing errors are the most probablelocations of crack initiation leading to fatigue failure.

Further, in high cycle fatigue, most of the fatigue lifetime is spent ininitiating the crack, and the thicker walls help reduce that crackinitiation. Moreover, fatigue cracks start in the wall sections that areunder the highest stress. In the walls 29 p the locations of maximumstress are known as explained above, and that allows steps to be takento reduce stress concentrations. For example, in order to reduce thestress concentrations in these high-stress areas it is preferable thatthe sidewalls 29 p have fillets or rounded junctures (a points 86) withadjoining walls, on both the inside and outside of the walls 29 p, asshown in FIG. 8. Because the critical stress areas are known and can beeither reinforced or have stress-relieving steps applied to them, it isbelieved unnecessary with the vibratory element 26 p to require morethan a machined surface finish. The expense and effort of a polishedsurface is not believed necessary.

Additionally, necking is also not a severe problem with the vibratoryelements 26 p because of the non-uniform stress distribution across thethickness of the sidewalls 29 p. The vibratory element 26 p also has anadvantage in that the spring constant of the sidewalls 29 p, the axialforce divided by axial deflection, is lower compared to the sidewalls 26of FIG. 7 a. A lower spring constant allows the piezoelectric element 22to expend more energy in moving the driven element 42 rather thanpushing against the preload spring formed by sidewalls 29, 29 p. Forthese reasons, it is advantageous to use curved sidewalls 29 p ratherthan straight, uni-axial tension sidewalls 29. The sidewalls 29 p arepreferably of uniform curvature, and symmetric about the portion of thelongitudinal centerline 25 p extending through the opening 28 p. Incomparison to straight sidewalls, curved sidewalls also allow theopening 28 to be dilated by a larger amount (elastically orplastically).

Wedging Preload Methods & Designs:

Referring to FIGS. 9–11, a method and apparatus using a wedging effectis described using a resonator of the configuration of FIG. 1. Theresonator 24 is thus illustrated as a rectangular body with arectangular opening 28 both symmetrically aligned along longitudinalaxis 25. Other shapes could be used. The opening 24 is slightly largerthan the piezoelectric element 22 and any protective cap 84, measuredalong the longitudinal axis as reflected in FIG. 10. A slight press-fitis also acceptable. A hole 90 is placed through the resonator 24 at oneend of the opening 28. The hole 90 is shown here as being placed in theend of the resonator 24 opposite the driving end 44 (FIG. 1) andadjacent the end connected to spring 50 (FIG. 1).

As shown in FIGS. 10–11, a wedge 92 is forced into the hole 90sufficiently to deform the hole 92 and the adjacent end of the opening28. As illustrated, the hole and wedge are both cylindrical, and locatedadjacent an end of the opening 28, so as to cause a bulging along thelongitudinal axis into the opening 28 sufficient to compress thepiezoelectric element 22 within the opening 28. Basically, the wedgedistorts one wall of the opening 28 to place the piezoelectric intocompression. The intervening protective plate 34 (FIG. 1) could be usedon one or both ends of the piezoelectric element 22, or omitted.

Because the dimensions of the cylindrical hole and wedge can be closelycontrolled and positioned on the resonator 24, and because the materialproperties of the parts are known and predictable, a precise deformationof the opening 28 can be achieved. The distortion must be symmetricallyachieved if the forces in sidewalls 29 are to be kept equal. But if anoffset compression is desired in order to potentially skew the axisalong which the force of the piezoelectric element 22 acts relative tothe resonator 24, then the hole 90 can be offset from the longitudinalaxis 25.

Referring to FIGS. 12, the hole need not be circular, but could comprisea rectangular slot, with the wedge 92 being correspondingly configuredto distort the hole 90 as needed to create the appropriate preload. Awedge 92 with a rectangularly shaped cross-section, or with anelliptically shaped cross section, could be used. As the shape of thewedge 92 changes to increase the amount of deformed material, the forceneeded to insert the wedge 92 into the hole 90 increases.

As discussed later, there are advantages in some situations if thepiezoelectric element 22 applies its force along an axis either parallelto but offset from the longitudinal axis 25 of the resonator 24, or at askew angle relative to that longitudinal axis 25. FIGS. 13–16 illustrateseveral ways to achieve this offset and skewing of the relativelongitudinal axes of piezoelectric element 22 and resonator 24. Anothervariation is discussed later regarding FIG. 53.

FIG. 13 shows the piezoelectric element 22 offset within the opening 28so the centerline 95 of the longitudinal axis of the piezoelectricelement 22 is laterally offset from the centerline of the axis 25 ofresonator 24. The offset can be above, below, or to either side of thecenterline 25, depending on the desired motion of the selectedcontacting portion 44.

FIG. 14 shows a small, hardened insert 94 interposed between one end ofthe piezoelectric element 22 and the adjacent wall of the opening 28. Ahardened steel ball or a small disk could be used, but it must be sizedor shaped relative to the abutting portions of the resonator so that nounacceptable deformation of the insert 94 occurs under driving forcesapplied by the piezoelectric element 22. In this embodiment a protectivecap 34 is preferably used in order to avoid localized forces on the morebrittle piezoelectric element 22 that might damage the piezoelectric.The location of the insert 94 can be above, below, or to either side ofthe centerline 25, depending on the desired motion of the selectedcontacting portion 44. More than one insert can be used.

FIG. 15 shows the opening 28 and piezoelectric element 22 aligned alongaxis 95 of the piezoelectric element 22, but both located at a skewangle relative to longitudinal axis 25 of the resonator 24. This resultsin an asymmetrical mounting of the piezoelectric element 25 relative tothe centerline of the resonator 24. The amount of skewing of therelative axes of the piezoelectric element 22 and the resonator 24 willdepend on the desired motion of the selected contacting portion 44. Thisconfiguration has the disadvantage of creating sidewalls 29 having avarying cross-section. But given the present disclosure, it is possiblefor one skilled in the art to mount the piezoelectric element 22 at askew angle to the longitudinal axis 25 of the resonator 24 and thevibratory element 26. Placing small inserts 94 on opposing ends of thepiezoelectric element 22 (see FIG. 16), and on opposing sides of thelongitudinal axis 25, could also achieve a skew axis of thepiezoelectric element 22 relative to axis 25. Various combinations ofthe above, and later described mounting systems can be used.

Mounting Of Vibratory Elements & Driven Elements

Given the present disclosure, a variety of mounting configurations arepossible for the vibrating element 26 and resilient mounting system 50.The mounting configuration is often determined by the location of theselected driving portion 44 and the mating engaging portion of thedriven element 42, and the required motion of those elements.

Referring to FIG. 17, the vibratory element 26 is mounted to a distalend of a rigid beam 102 that is pivotally mounted at a pivoted end torotate about pivot point 104. The vibratory element 26 has a selectedcontacting portion 44 resiliently urged against the driven element 42.The selected contacting portion 44 is shown inward of the distal end 36of the vibratory element 26 to reiterate that the location of theselected contacting portion 44 can be at various locations on thevibratory element 26. The same applies for the other mountingconfigurations discussed herein.

As illustrated in FIG. 17, spring 50 resiliently urges the parts tomaintain sufficient contact during the desired portion of the motion tomove the driven element. The spring 50 may take various forms and beconnected in a variety of ways. The driven object 42 can have a varietyof shapes, or motions. Useful forms of driven objects 42 comprise one ofa rod, a ball or a wheel that is located at a distal end of thevibratory element 26. The driven element 42 needs to be appropriatelysupported to allow its intended motion, and that support is not shownhere as the motion can vary according to design.

FIG. 18 shows an arrangement similar to FIG. 17, but with the locationof the resilient force altered so that it is exerted on the distal endof the pivoted rigid element 102 and pulls the vibratory element 26 intocontact with the driven element 42 rather than pushing it into contact.The spring 50 applying the resilient force advantageously applies itsurging force along an axis aligned with the longitudinal axis 25 of thevibratory element 26, but that is optional.

FIG. 19 shows an arrangement similar to FIGS. 17–18, but with thelocation of the resilient force altered so that it is exerted adjacentto the pivoted end of rigid element 102. The location of the resilientforce, such as applied by spring 50, can affect the displacement of thespring. When the spring 50 is located nearer the pivot point 104, thespring 50 does not move much because the effective moment arm betweenthe pivot point and the connection to the spring is less.

If the vibratory element 26 is rigidly mounted, configurations similarto those described herein can be used to resiliently urge the drivenelement 42 to maintain sufficient contact with the fixedly mountedvibratory element 26 to achieve the desired movement of the drivenelement.

FIG. 20 shows one advantageous mounting configuration that uses a flatstrip of spring metal for the spring 50. The spring 50 has a first end50 a mounted to a base 52, and an opposing end 50 b connected to thevibratory element 26. A first leg of the spring 50 containing end 50 ais parallel to the longitudinal axis 25 of the vibratory element 26,with the second leg of the spring being bent at about a right angle. Thedistal end of the vibratory element 26 is resiliently urged against thedriven element 42. The driven element 42 can in principle have anysufficiently smooth shape, but readily useful forms of driven objects 42comprise one of a rod, a ball or a wheel that is located at a distal endof the vibratory element 26. The driven element 42 needs to beappropriately supported to allow its intended motion, and that supportis not shown here as the motion can vary according to design.

FIG. 21 shows a straight, leaf spring 50 a having one end rigidlymounted to base 52, with an opposing distal end 50 b mounted to thevibratory element 26. The distal end of the vibratory element 26 isurged by the spring 50 against the driven element 42. Other shapes ofsprings 50 are possible.

FIG. 22 shows a vibratory element 26 having a first end pivoted aboutpivot 106 and an opposing distal end resiliently urged by spring 50against a driven element 42. The selected contacting portion 44 isintermediate the pivot point 106 and the connection of spring 50 alongthe longitudinal axis 25, and is on an opposing side of the axis 25 asis the spring 50 and pivot 106. But various locations of the selectedcontacting portion 44 relative along the axis 25 are possible, dependingon the desired motion and the configuration of the parts.

There is thus provided a method and apparatus for generating at leasttwo components of motion at the selected contacting portion 44. Thesetwo motion components have mutually different directions, with eachcomponent oscillating when the piezoelectric element 22 is excited at apredefined frequency, and with the two components having mutuallydifferent phases. These two motion components are shaped so as to createan elliptical motion 100 along a desired orientation, by configuring thevibratory element 26, its suspension 50, or both. There is alsoadvantageously provided a method and apparatus by which the same orother contacting portions 44 create suitable ellipses 100 at variousexcitation frequencies of the piezoelectric element 22, resulting inmutually different macroscopic motions of the driven body 42 engagingone or more of the selected contacting portions(s) 44.

In one embodiment, the vibration element 26 is attached to the base 52with a spring-like element 50, wherein the spring can be of the bending,torsion, pneumatic, elastomeric, or any other type. The spring could forexample be made from portions of an electronic circuit board, which hasadvantages in manufacturing. The spring constant or flexibility of thespring can be adjusted to compensate for wear in the contact areabetween contacting portion 44 and the engaging portion of the drivenelement 42, and can also compensate for production inaccuracies. Forinstance, high compliance of the spring 50 results in small variationsin the resilient contact force the contacting portion 44 exerts on thedriven element 42 despite relatively large deflections of the contactingportion 44.

The spring 50 can be attached to the vibration element 26 in manydifferent ways. In one embodiment, the vibration element 26 contains anopening 28 with a dimension slightly smaller than the sum of acorresponding dimension of the undeformed piezoelectric element 22 andthe thickness of the spring 50. Inserting the spring 50 and thepiezoelectric element 22 into the opening 28 causes the opening toexpand, thus creating a press-fit that functionally connects saidvibration element to the spring and the piezoelectric element. Inanother embodiment, the vibration element contains an opening, such as aslot, into which an end of the spring can be pressed, glued, screwed, orotherwise fastened. The slot can be oriented in any preferable way. Inone embodiment, the slot is oriented perpendicular to the longitudinalaxis 25 of the vibrating element 26. In another variation, it isoriented parallel thereto.

In addition to connecting the vibration element 26 to the housing orbase 52, the spring-like element 50 can also be a functional extensionof the vibration element 26. With proper adjustments, the spring 50 canisolate the vibrations of the vibration element 26 functionally from thehousing 52. Also, the spring 50 can influence the dynamic behavior ofthe vibration element 26 in order to enhance the performance of thevibration element 26 through amplification or other dynamic effects. Forinstance, if the spring 50 has axes of symmetry which are differentthan, or offset to those of, the axes of symmetry of the vibrationelement 26, then the assembly of the piezoelectric element 22, vibrationelement 26 and spring 50 becomes dynamically asymmetrical resulting in acoupling of what were formerly independent modes of vibration.

In a further embodiment, the vibrating element 26 can be attacheddirectly to the housing or base 52. It is preferable if the housing orbase 52 functionally isolates the vibrations of the vibrating element26. In this embodiment, the housing itself must exert the resilientforce that presses the vibrating element 22 against the moving element42. It is preferable if the design of the housing or base 52 provides amechanism to adjust the contact force and to compensate for motor wear.A screw in a slot to adjustably position the vibratory element 26relative to the driven element 42 is one example.

In yet another embodiment, the vibration element 26 is rigidly connectedto the housing 52, and the driven element 42 is resiliently urgedagainst the vibrating element 26 by the bearings in or on which themoving element is supported. For this purpose, it is preferable if thesupport contains some sort of spring or other compressible medium toprovide a resilient force to urge the parts into contact. In thissituation, the motor assembly 20 could also mounted in a position sothat gravity acting on the driven element 42 may provide the necessaryresilient force.

Locating Driving & Driven Elements

Referring to FIGS. 23–36, various configurations are shown for mountingthe vibratory element 26 relative to the driven element 42. Thesefigures are schematically shown, and omit the mounting systems of theparts that allow the desired motion and that maintain the parts insufficient contact for the intended use. For illustration the drivenobject 42 is shown as a rod with a cylindrical cross section, but itcould be a ball, a wheel, a rod, a bar, a gear or something else. Thevibratory element 26 needs to be urged against the driven object 42 witha certain force and angle to achieve the contact needed to cause motion.This can be achieved through the mounting mechanisms described earlieror apparent to those skilled in the art given the present disclosure.The mechanism causing that resilient contact is not shown. Also notshown is the mounting arrangement that allows the desired movement ofthe driven part 42 as that will vary with the particular design. Thefollowing arrangements are only examples. Others are possible but arenot described since it is not possible to cover all of them.Combinations of these arrangements are possible as well.

Single Vibratory Element Configurations: FIGS. 23–26 show configurationsusing a single vibratory element 26. In FIG. 23, the vibratory element26 is above the driven element 42, with at least one of the elements 26,42 being resiliently urged to maintain the selected driving portion 44in sufficient contact with the selected engaging portion of drivenelement 42 to achieve the desired motion. The longitudinal axes of thevibratory element 26 and the driven element 42 are perpendicular to eachother, but they could be at various intermediate angles. The contactportion 44 is inward of the distal end 36, but could be at an locationalong the length of the vibratory element 26 achieving the desiredmotion at a selected amplitude. The contact portion 44 is thusadvantageously selected to occur at a location having the desiredelliptical motion 100. The motion 100 is shown generally aligned withthe axis 25 of the vibratory element 26, which will cause rotation ofthe driven element 42 about axis 45. But that need not be the case, asit could be in a plane orthogonal to axis 25 to cause translation alongaxis 45, or at orientations in between, depending on the desired motionand the design of the components. As used herein, an alignment of about0–5 degrees will be considered to be aligned.

FIG. 24 shows the longitudinal axis 25 vertically offset from andperpendicular to the axis 45 of the driven element. Various intermediateangles of inclination are possible. The selected contact portion 44 isat the distal end 36, at a lower peripheral edge of the vibratoryelement 26. This arrangement lends itself to producing rotation of thedriven element 42 about axis 45, or translation along that axis, orcombinations of those motions.

In FIGS. 25–26, the longitudinal axes 25, 45 are coplanar and inclinedrelative to each other at an angle α as discussed relative to angle α ofFIG. 1. The selected contact portion 44 is at the distal end 36, at alower peripheral edge of the vibratory element 26. This arrangementlends itself to producing translation of the driven element 42 alongaxis 45, or rotation about that axis, or combinations of those motions.Referring to FIG. 26, the axes 25, 45 are shown as coplanar, but theyneed not be so and could intersect at skew angles.

Multiple Vibratory Element Configurations: Configurations using multiplevibratory elements 26 that cooperate to move the driven element 42 areshown in FIGS. 27–42. The use of multiple vibratory elements 26 has theadvantage of providing more locations of support to the driven element42 so that some of the bearings may be omitted. Thus, cost savings andfriction reduction that typically comes with low cost bearings orbushings are achieved. In some applications, it can be enough to suspendthe driven element 42 entirely using vibratory elements 26 without theneed for additional bearings. The vibration of the contacting portion ofthe vibratory element 26 can provide a low friction support, and anelliptical motion of the supporting portion of the vibratory element 26is not necessary for this low friction support application.

Further, the use of multiple vibratory elements 26 can accordinglymultiply the force, and/or the speed with which the driven element 42 ismoved. A single, common excitation signal could be provided to each ofthe vibratory elements 26 in order to simplify the electrical system, orseparate signals could be provided to cause different simultaneousmotions of the driven element 42.

In the following, configurations with a specific number of vibratoryelements 26 are described. Given the disclosures therein, a variety ofother mounting configurations can be configured that use multiplevibratory elements 26 to restrain various degrees of freedom of thedriven element 42.

Double Vibratory Element Configurations: Configurations usingspecifically two vibratory elements 26 and a single driven element 42are shown in FIGS. 27–36. In FIG. 27 there are two vibratory elements 26resiliently urged against opposing sides of driven element 42. The twovibratory elements 26 have axes 25 perpendicular to the longitudinalaxis 45 of driven element 42, and on opposing sides of that axis 45. Theselected contacting portion 44 of each vibratory element 26 a, 26 b ispreferably intermediate the distal ends of the vibratory elements, butthat need not be the case as the contacting portion 44 could be atdistal end 36. The axes 25 of the vibratory elements 26 can be paralleland coplanar, but they do not have to be either parallel or coplanar.This arrangement lends itself to producing translation of the drivenelement 42 along its longitudinal axis 45, or rotation about that axis,or combinations of those motions.

FIG. 28 shows two vibratory elements 26 resiliently urged against acommon side of driven element 42. The two vibratory elements 26 haveaxes 25 perpendicular to the longitudinal axis 45 of driven element 42,but the axes 25 could be inclined to axis 45. The axes 25 of thevibratory elements 26 can be coplanar, but need not be so. The contactportions 45 are at distal edges of each face 36. The contact portion 44is at an angle 45 degrees from the horizontal plane in which the axis 45is shows as being located, but on opposing sides of that plane. Thisconfiguration lends itself to producing translation of the drivenelement 42 along its longitudinal axis 45, or rotation about that axis,or combinations of those motions.

FIG. 29 shows a configuration similar to FIG. 28 except that thevibratory elements 26 face each other and are located on opposing sidesof the driven element 42 relative to the vertical axis.

FIG. 30 shows a configuration similar to FIG. 24, except there are twovibratory elements 26 on opposing sides of the driven element 26, on acommon axis 25. The longitudinal axes 25 of each vibration element 26need not coincide, but could be coplanar and skewed relative to eachother.

FIG. 31 has two vibratory elements 26 on opposing sides of the drivenelement 42, with the elements 26 facing each other but oriented atinclined angles α, β, respectively, relative to a plane through thelongitudinal axis 45 of driven element 42. The angles α, β are shown sothe axes 25 of each vibratory element 26 are parallel, but they need notbe parallel. The angles preferably cause the longitudinal axes 25 tointersect the longitudinal axis 45 of the driven element 42, but neednot do so. The selected contact portion 44 is at the distal end 36 ofeach vibratory element 26.

FIG. 32 has two vibratory elements 26 on opposing sides of the drivenelement 42, with the elements 26 facing the same direction and orientedat inclined angles α, β, respectively, relative to a plane through thelongitudinal axis 45 of driven element 42. The angles α, β are such thatthe longitudinal axes 25 preferably intersect longitudinal axis 45 ofthe driven element 42, but need not do so. The selected contact portion44 is at the distal end 36 of each vibratory element 26.

FIG. 33 has two vibratory elements 26 on the same side of the drivenelement 42, with the elements 26 facing the same direction andorientated at inclined angles α, β, respectively, relative to a planethrough the longitudinal axis 45 of driven element 42. The angles α, βare such that the longitudinal axes 25 preferably intersect longitudinalaxis 45 of the driven element 42, but need not do so. The axes 25 neednot lie in the same plane, but preferably do so. The selected contactportion 44 is at the distal end 36 of each vibratory element 26.

FIG. 34 has two vibratory elements 26 on the same side of the drivenelement 42, with the elements 26 facing each other and oriented atinclined angles α, β, respectively, relative to a plane through thelongitudinal axis 45 of driven element 42. The angles α, β are such thatthe longitudinal axes 25 preferably intersect longitudinal axis 45 ofthe driven element 42, but need not do so. The axes 25 need not lie inthe same plane, but preferably do so. The selected contact portion 44 isat the distal end 36 of each vibratory element 26.

FIGS. 35–36 show a configuration with two vibratory elements 26 onopposing sides of the driven element 42, with the elements 26 facing thesame direction and orientated at inclined angles α, β, respectively,relative to a plane through the longitudinal axis 45 of driven element42. The angles α, β are such that the longitudinal axes 25 preferablyintersect longitudinal axis 45 of the driven element 42, but need not doso. The axes 25 need not lie in the same plane, but preferably do so.Advantageously, the axes 25 intersect at a common location on axis 45,with the engaging portions 44 being in the same plane orthogonal to axis45.

In this configuration, the selected contact portion 44 is at the distalend 36 of each vibratory element 26. The selected contact portions 44 ofeach element 26 are configured to have a shape mating with the shape ofthe engaged portion of driven element 42. Here, the circularcross-section of rod 42 results in a convex curved surface for theselected contacting portions 44. This curved engagement results in thevibratory elements 26 providing a support for the driven element 42 thatrestrains motion except for translation along axis 45. If the contactingportion 44 has a small engaging surface along the length of axis 45,then the driven element 42 will rock about the engaging portions 44. Ifthe contacting portion 44 has an engaging surface with a sufficientlength along the length of axis 45, then the driven element 42 can besupported without rocking about the engaging portions 44. Thisconfiguration can simplify the mounting of the driven element 42 byallowing the vibratory elements 26 to also act as bearings by clampingthe rod between the tips of two vibratory elements 26.

Triple Vibratory Element Configurations:

FIGS. 37–40 show configurations using three vibratory elements 26 a, 26b and 26 c, with the letters a, b, and c being associated with thevarious corresponding parts of the first, second and third vibratoryelements, respectively. FIG. 37 shows two vibratory elements 26 a, 26 bas described in FIG. 27, each of which is resiliently urged againstopposing sides of driven element 42. The two vibratory elements 26 a, 26b each have axes 25 perpendicular to the longitudinal axis of drivenelement 45, and on opposing sides of that axis 45. The selectedcontacting portion 44 a, 44 b of each vibratory element 26 a, 26 b ispreferably intermediate the distal ends of the vibratory elements, butthat need not be the case as the contacting portion 44 could be atdistal end 36. A third vibratory element 26 c is located on an opposingside of the driven element 42 with its selected contacting portion 44 cintermediate, and preferably equally between, the contacting portions 44a, 44 b along an axis between 44 a and 44 b. The driven element 42 hasits longitudinal axis along the z axial direction. Preferably, the firstand second vibratory elements 26 a, 26 b contact the driven element 42at the 12 and 6 o'clock positions, with the third vibratory element 26 ccontacting the driven element 42 at the 3 o'clock position. Othercontact locations are possible. The contacting portion 44 c ispreferably at a distal edge of the vibratory element 26 c, with thethird vibratory element 26 c being oriented at an angle α parallel tothe plane containing axes 25 a, 25 b. The axes 25 of the vibratoryelements 26 a, 26 b are preferably parallel and the axes 25 a, 25 b and25 c are preferably coplanar, but the various axes do not have to beeither parallel or coplanar. This configuration provides for translationand rotation of the driven element 42 along and about its longitudinalaxis 45, with the vibratory elements restraining translation in bothdirections along the y-axis, and in the +x direction, but allowingmotion along the −x direction.

FIG. 38 shows the vibratory elements 26 with their longitudinal axes 25perpendicular to a radial axis extending in a plane orthogonal to theaxis 45 of the driven element 42. The contacting portions 44 areillustrated as offset from distal ends 36, but that need not be thecase. The vibrating elements 26 are shown as equally spaced with anglesβ, γ, and α each being about 60 degrees, but the angles can vary. Theaxes 25 a, 25 b, 25 c are shown as coplanar, but they need not be so.The driven element 42 has its longitudinal axis along the z axialdirection. This arrangement allows the vibrating elements 26 to restraintranslation of the driven element 42 in both directions along the x-axisand y-axis.

FIG. 39 places two of the vibratory elements 26 a, 26 b on one side ofthe driven element with axes 25 a, 25 b parallel to the x-axis, and withtheir respective contacting portions 44 a, 44 b engaging the peripheralportion of the driven element at corresponding locations along an axisparallel to the vertical y-axis. The contacting portions are located atedges of the distal ends 36 a, 36 b. The axes 25 a, 25 b are paralleland coplanar, but need not be coplanar or parallel. The third vibratoryelement 26 c is on the opposing side of the driven element 42, with axis25 c parallel to the y-axis. The axis 25 c is preferably coplanar withaxes 25 a, 25 b, but need not be so. The driven element 42 has itslongitudinal axis along the z axial direction. This arrangement allowsthe vibratory elements 26 to restrain translation of the driven element42 in both directions along the x-axis and y-axis.

FIG. 40 places two of the vibratory elements 26 a, 26 b on one side ofthe driven element with axes 25 a, 25 b parallel to the x-axis, and withtheir respective contacting portions 44 a, 44 b engaging the peripheralportion of the driven element at corresponding locations along an axisparallel to the vertical y-axis. The axes 25 a, 25 b are parallel andcoplanar, but need not be coplanar or parallel. The driven element 42has its longitudinal axis along the z axial direction. The thirdvibratory element 26 c is on the opposing side of the driven element 42,with axis 25 c parallel to the x-axis, and coaxial with axis 25 b. Thecontacting portions are located at edges of the distal ends 36 a, 36 b,36 c. This arrangement allows the vibratory elements 26 to restraintranslation of the driven element 42 in both directions along the x-axisand y-axis, but does permit motion along one direction of a skew axis at45 degrees from the horizontal as shown in FIG. 40.

In the above configurations using multiple vibratory elements 26, eachvibratory element is preferably activated at the same time as the othervibratory elements so that the vibratory elements cooperate to producethe desired motion of the driven element 42. But the vibratory elements26 could be separately activated at different times or in differentcombinations or in different sequences in order to achieve separatemotions of the driven element.

Six Vibratory Elements:

FIGS. 41–42 show a configuration in which six vibratory elements 26 athrough 26 f are used to support a driven element 42 that can rotate andtranslate about its longitudinal axis 45. The vibratory elements 26 eachhave one end attached to a ring 110 that encircles the driven element42, preferably in a plane orthogonal to the longitudinal axis 45 of thedriven element. The opposing distal end 36 a through 36 f of thevibratory elements 26 is pressed against driven element 42. Three of thevibratory elements 26 extend toward the driven element 42 in directionsopposite to the other three vibratory elements as best seen in FIG. 42.The relative position of each vibratory element 26 viewed in the x-yplane orthogonal to the axis 45 of driven element 42 (FIG. 41), isdetermined through the angles α, β, γ, σ, ε, and ρ. These angles arepreferably 60 degrees in order to equally distribute the support anddriving forces, but the angles can be different from that. The vibratoryelements 26 advantageously have their longitudinal axes 25 intersectingthe longitudinal axis 45 of the driven element 42, but the axes 25 couldbe skewed so they do not intersect the axis 45. The angles between thevibratory elements 26 and the driven element 42 are defined by δ and φas shown in the drawing, and will vary depending on the dimensions ofthe various parts and on the orientation of the vibratory elements 26.The flexibility of the ring 110 helps to ensure that the vibrationelements 26 are pressed against the driven element 42. As a result therod is suspended at six points.

This configuration allows the vibratory elements 26 to support thedriven element 42 so as to allow translation only along the longitudinalaxis 45 of the driven element 45 and to allow rotation about that axis.

Motor Operating Principles

The following description helps understand the operation of theabove-described embodiments, and helps understand the variety of ways toimplement these embodiments and variations thereon.

The present motor uses only one piezoelectric element 22 with oneelectrical excitation signal to excite various modes of vibration of thevibration element 26. The motion of the contact portion 44 is determinedby these modes of vibration. In particular, the present motor achievesan elliptical movement of the contact portion 44 in a first directionfor a sinusoidal electrical excitation signal at a first frequency, andan elliptical movement of the contact portion 44 in a second directionfor a sinusoidal excitation signal at a second frequency, providing arequired force or amplitude of motion or speed at the contact portion44. Elliptical movements of the contact portion 44 in a third and moredirections for sinusoidal excitation signals at third and morefrequencies are known to be possible.

The motor assembly 20 is advantageously configured so that the contactportion 44 traces the elliptical motion several tens of thousand timesper second to make motor operation inaudible for humans and most petanimals. During a selected segment of each elliptical cycle, the contactportion 44 comes into contact with the engaging surface of the drivenobject 42 where it exerts a frictional contact force that transports thedriven object 42 by a small amount into a corresponding direction. Theobserved macroscopic motion of the driven object 42 is the accumulationof all individual transportation steps.

While the bulk of this disclosure refers to a contact portion 44 locatedat a distal end 36 of vibration element 26 and moving in a firstelliptical path 100 a causing the driven object 42 to be transported indirection of the driven object's longitudinal axis 45, and the sameselected contact portion 44 moving in a second elliptical path 100 bcausing transportation in an opposing direction (as in FIGS. 2 and 5),the first and second selected contacting portions 44 need not be thesame, need not be adjacent, and need not be located at a distal end 36.They need only be located on the same vibratory element 26. Further, thenumber of selected contacting portions 44 and the directions andorientations of respective elliptical paths 100 at each contactingportion can vary according to the particular design. There could bethree, or there could be more. There can thus be a plurality of selectedcontacting portions 44 on the vibratory element 26 moving in a pluralityof elliptical paths 100 in a plurality of directions.

Advantageously the desired motion of a selected contact portion 44 isidentified, whether it is in a single direction or multiple directions,and whether there is a single selected contact portion 44 or severalcontact portions 44, or combinations thereof. The motor assembly 20 isthen designed to achieve that motion. As often occurs, the design doesnot achieve perfection but instead achieves an acceptable approximationof the desired motion. A number of the factors that can be used toconfigure the components of motor assembly 20 to achieve that desiredmotion are discussed below.

Generation of Elliptical Motion: If the piezoelectric element 22 isexcited with a sinusoidal electrical signal, it generates a sinusoidalforce and a sinusoidal displacement principally along its longitudinalaxis 95, shown in FIGS. 1–3 as being alongside longitudinal axis 25 ofthe vibration element 26, or shown in FIG. 15 as being at an obliqueangle to the longitudinal axis 25. Said force and displacement are thenused to excite modes of vibration of the vibration element 26. Thevibration element 26 is preferably configured so that at a predeterminedexcitation frequency at least two of its modes of vibration aresubstantially excited. If a mode has only a uniform motion component inthe direction of the longitudinal axis 25, it is considered to be alongitudinal mode. If the motion components of a mode lie in a directionperpendicular to the longitudinal axis 25, the mode is considered to bea bending mode. Further well known modes include torsion and shearmodes. A mixed mode is neither of these modes but can have components ofmotion in, or rotating around, any of the directions 25, 38 or 40. Eachmode that is excited adds a sinusoidal motion component to the motion ofthe contact portion 44. If at least two of these components of motionare non-parallel and mutually out of phase, the resulting motion of thecontact portion 44 is known to be elliptical.

The bulk of this disclosure refers to a piezoelectric element 22 thatgenerates force and displacement principally along its longitudinal axis95, but a piezoelectric element having a different principal direction,or a force and displacement-generating element other than apiezoelectric element, could be used.

Making Use of Elliptical Motion: It is an advantage of the presentinvention over prior art motors that elliptical motions do not have tobe achieved exclusively with mutually perpendicular longitudinal andbending modes that are excited 90 degrees out of phase, but instead thatthe elliptical motion can be generated with at least two excited modesthat can be mutually oblique and have a phase difference that can besubstantially different from 90 degrees. In this case, the contactportion 44 traces an ellipse 100 whose semi-axes are not necessarilyaligned with any of the directions 25, 38 or 40, thus making itadvantageous for the vibration element 26 to be mounted at an obliqueangle to the driven object 42. That is, the longitudinal axis 25 ispreferably inclined to the vibration element 26 at an angle α (FIG. 1),which will vary with the particular design and components involved.Oblique mounting of the vibration element 26 rotates the ellipse 100with respect to the driven object 42. Associated with this rotation, acoordinate transformation is formulated elsewhere that exposes thebeneficial and enhancing effects of this rotation on relative phaseshifts between components of motions that generate the elliptical path100.

While the elliptical motion 100 of the selected contacting portion 44 isachieved even if the selected contacting portion 44 is not engaged withthe driven element 42, in order to achieve useful motion the contactportion 44 of vibration element 26 is placed in physical contact withthe engaging surface of the driven object 42 during a certain portion ofeach elliptical cycle 100. This portion preferably remains the same foreach subsequent cycle. During each engagement, the vibration element 26exerts frictional forces on the driven object 42. These forces can varyover the period of an engagement but their accumulative effecttransports the driven object 42 relative to vibration element 26. It isbelieved that this transport is most efficient if the direction oftransport coincides with the direction of motion of the contact portion44 at the point of the ellipse that is closest to the driven object 42.

The speed of contacting portion 44 tangential to the elliptical path 100is largest where the minor-axis of the ellipse intersects the ellipticalpath, and smallest where the major axis of the ellipse intersects theelliptical path. An ellipse whose major axis is tangential to theengaging surface of driven object 42 is therefore expected to provide anefficient transportation mechanism. It can be beneficial to use anellipse whose major axis is inclined with respect to the engagingsurface of driven object 42. In this situation, the contact portion 44moves towards the driven object 42 at a different rate than the rate atwhich it moves away from it after having passed the point closest todriven object 42. Inherent to the elliptical shape, a faster approachtypically results in a slower retreat and vice versa, so that theprocess of engagement with the driven element 42 can be selected to bemore gradual or more abrupt. At its extreme, such a motion is known as asaw-tooth motion. Motors that generate exact saw-tooth motion are in theprior art. Purposefully employing an inclined ellipse in the presentdisclosure provides therefore some of the advantages only seen in thosesaw-tooth motors.

To ensure efficiency of transport, it is preferable that the frictionalengagement is sufficiently large, and that the contacting portion 44moves against the direction of desired transport of driven object 42only while the friction forces are reduced or vanish, which occurs whensome or all of the contact portion 44 has lost contact with the engagingsurface of the driven object 42.

The amount of friction and wear depends also on the friction parametersand the material combination used for the contact portion 44 and thesize of contact portion 44. These parameters also influence the strengthof the motor 20. More friction typically results in stronger force butmay also result in more wear. Material combinations that are believedsuitable for use include steel, aluminum and glass on one side of thecontact, and glass, fiberglass, PMMA, PVC, ABS or steel on the otherside of the contact. The friction parameters of glass surfaces aremodifiable chemically or physically by adding particles or etching atexture.

It is an advantage of the motor assembly 20 that the dimensions of theengaging surface of the driven object 42 do not have to be precise andthat variations are accommodated by the resilient mounting system of themotor 20, which is discussed later. Also, it has been shown that weardue to the vibrations can modify the contact portion 44 of vibrationelement 26 and create a larger contact area. This effect is especiallystrong at the beginning of the lifetime of the motor. The effect fadesquickly, resulting in better motor performance. This wear can be used toadvantage since the resilient mount 50 urges the selected contactingportion 44 against the driven element 42, allowing for wear-in betweenharder and softer materials, that can reduce initial manufacturingtolerances. As desired, the wear-in can also be used to increase theselected contacting area 44.

Achieving desired elliptical motion: The size and orientation of theelliptical trajectory 100 depend on the amplitudes and phases used togenerate the ellipse. The ability to maintain a useful ellipticaltrajectory 100 of contact portion 44 over a sufficiently large frequencyrange depends on the vibration design properties of the motor assembly20.

It is known that a mode of the vibration element 26 undergoes a smoothphase change of −180 degrees with respect to the excitation signalapplied to the piezoelectric element 22 if the frequency of excitationis increased across the resonance frequency of the mode. The width ofthe frequency range within which this transition occurs increases withthe amount of mechanical damping in the system. It is desirable thatsuch a frequency range is sufficiently large in order to assure that thephase difference between two excited modes can remain sufficientlydifferent from 0 or 180 degrees over an extended frequency range and canpotentially sustain a desired elliptical motion of the contact portion44. This renders the motor 20 in principle less sensitive to variationsin manufacturing and operating conditions. In order to achieve a desiredamount of damping at a particular location, a separate dampening elementcould be added to any part of the vibration element 26 or the portion ofthe suspension that participates in the mechanical vibrations. Butpreferably the damping that is inherent in the system design andmaterials is used.

To achieve a stronger motor, it is also desirable if the excited modesof vibration show significant amplitudes at the contact portion 44 nearthe desired frequency of excitation and thus it is preferable to have afrequency of excitation that is close to a resonance frequency of aselected mode. Since the amplitude of a mode at the contact portion 44also depends on the amplitude of its excitation, it is preferable thatthe vibration element 26 is designed to appropriately distribute themechanical vibrations generated by the piezoelectric element 22 to thevarious modes. This distribution can be achieved in a controlled fashionin a number of ways using combinations of damping, geometric andmaterial properties of the vibration element 26, and the forces that aregenerated between the vibration element 26 and the driven object 42 atthe contact portion 44. Conceptually, methods and modifications thataffect the force distribution are different from methods that affect theshape of a mode and its resonance frequency. In reality however, amodification that affects force distribution very often modifies also amode shape and its resonance frequency. For example, it is known for arod-like vibration element 26 that some modifications that woulddistribute mechanical energy forces to a pure longitudinal and a purebending mode would typically also couple the two modes together tocreate new modes of mixed type.

Distributing Mechanical Vibrations: Internal damping forces can coupleone mode to another so that the piezoelectric element 22 can potentiallydrive a first mode, which in turn excites a second mode indirectly byway of damping. This effect is particularly strong if the respectiveresonance frequencies and the frequency of excitation lie closetogether.

A first mode that is excited by the piezoelectric element 22 at acertain frequency can excite a second mode also by way of the contactforces generated in the contact portion 44. Specifically, the ellipticalmotion of the contact portion 44 can produce a force that is sinusoidalor a force that is intermittent with the same frequency that drives thefirst mode. This force then excites other modes in the vibration element26, as well as vibration modes of the driven object 42 discussedelsewhere. This form of excitation can be mutual, and this effect can bedeliberately used, so that formerly independent modes can be coupledtogether to form new modes. The orientation of the ellipse 100 at thecontact portion 44 and the portion of the ellipse during which contactforces are generated determine the phase with which a second mode isexcited relative to the first mode. This phase is preferably not amultiple of 180 degrees.

Which modes of vibration element 26 are excited by way of contact, andby how much they are excited, also depends on the position andorientation relative to vibration element 26 of contact portion 44 andengaging surface of driven object 42. The contact portion 44 can bechosen to lie in a plane of symmetry of the assembly 20, vibrationelement 26, resilient mounting system 50 or driven object 42, or not.Non-symmetric positioning can be used to excite modes that otherwisewould be harder to excite by the piezoelectric element 22 alone, forexample certain bending modes or torsion modes of vibration element 26.To the same end, the orientation of the engaging surface relative tovibration element 26 can be chosen to be perpendicular or parallel tocertain planes of symmetry, or not.

Location and Orientation of Piezoelectric Element: Referring to FIG. 1,the vibrating element 26 preferably has an elongated, rod-like shapewith an opening 28 perpendicular to the longitudinal axis 25 of the rod.The opening 28 has dimensions slightly smaller than correspondingdimensions of the piezoelectric element 22, so that the piezoelectricelement can be inserted into the opening 28 in a press-fit manner. Ifthe vibrating element 26 has a symmetric shape, and if the piezoelectricelement 22 is inserted symmetrical with respect to the longitudinal axis25, and if the contact between the piezoelectric element 22 and thevibration element 26 is nearly perfect, then it is expected thatprimarily only longitudinal vibrations in direction of axis 25 aregenerated. These vibrations can be transformed into bending or othervibrations by way of the previously discussed contact forces at contactportion 44, or they can be transformed by the action of the resilientmounting system 50 discussed below, which urges vibration element 26against the driven object 42.

The piezoelectric element 22 can directly generate other thanlongitudinal vibrations in the vibration element 26 if element 22 isnon-symmetrically inserted into the opening 28, e.g., if thelongitudinal axis 95 of the piezoelectric element 22 is offset (cf. FIG.14) or inclined (cf. FIG. 15) with respect to the longitudinal axis 25of vibration element 26, or if at least one of the contact areas betweenthe piezoelectric element 22 and the resonator 24 is madenon-symmetrical. For example, the vibration element 76 in FIG. 5 has thelongitudinal axis of the piezoelectric element 22 offset from aprincipal longitudinal axis of the resonator 74. This offset couplesvarious modes of the resonator 74 and the vibration element 76.Moreover, the resonator 74 rotates about pin 78, and that may furthermodify vibrating modes of the vibrating element 76.

The more pronounced the modifications are that let the piezoelectricelement 22 be inserted in a asymmetric fashion, the more bending andother vibrations are typically excited. Also, such modificationstypically couple formerly independent longitudinal and bending modestogether to create new modes of mixed type. Torsion modes in a rod-likevibration element could also be excited.

In a preferred embodiment, the piezoelectric element 22 is inserted intothe opening 28 in the resonator 24 such that the resonator and thepiezoelectric element 22 do not enter into perfect contact along theentire area where contact could be possible. To achieve such apurposefully partial contact during the insertion process, the sidewalls29 of the opening 28 could for example be deformed by the insertedpiezoelectric element 22 such that contact is lost in certain portionsof the potential contact area. Alternatively, partial contact can beachieved by making the potential contact surface of the piezoelectric 22non-even, for example by removing material in parts of the contact areaof the resonator 24 before inserting the piezoelectric into the opening28. In FIGS. 10 and 11, this could also be achieved by inserting a pin92 at a location offset from the depicted longitudinal axis 25. Also,inserts 94 (FIG. 16) could be used to provide localized contact areas atthe location of the insert. Moreover, combinations of the above methodsmay be used to achieve a desired partial contact and to induce a desiredcombination of lateral and longitudinal motion components at a desiredcontacting portion 44.

Shape of Vibration Element: The resonance frequencies of the variousvibration modes typically decrease if the vibration element 26 is madelonger, and vice versa. Also, the shape and size of the cross-sectionsof the resonator 24 affect the resonance frequencies and modes involvingbending and torsion. For example, referring to FIG. 73, thecross-section of the resonator 24, or at least of a portion of thedistal end of the resonator 24 could be I-shaped, which can be used tovary the relative stiffness and resonance frequencies of modes involvinglongitudinal motion and lateral bending since the I beam cross-sectioncan have the stiffness along one lateral axis much different than thestiffness along the other lateral axis. It also produces a lower lateralbending stiffness without having to greatly increase the length of theresonator 24. FIG. 73 also shows a T-shaped cross section, which couldintroduce a twisting mode if the T was made non-symmetric about itsvertical axis. C-shaped cross-sections and variety of othercross-sectional shapes can be used to vary the resonance modes of theresonator 24 and of the vibrating element 26. Other non-symmetric,cross-sectional shapes can be used.

To purposefully achieve modes of vibration that can generate a desiredelliptical motion 100 at the contact portion 44 of vibration element 26so that the ellipse 100 is inclined with respect to the longitudinalaxis 25 of vibration element 26 and/or the engaging surface of drivenobject 42, it can be advantageous to have a non-symmetric design of thevibration element 26. For example, the resonator 24 could be madehelical, or it could have an arched or an L-shape. Other shapes arepossible. The asymmetric mass distribution that is achieved this wayresults in modes of vibration that are neither purely longitudinal norpurely transversal in nature, which is beneficial for generatinginclined elliptical motion 100.

Moreover, referring to FIG. 77 a further embodiment is shown that hasadvantageous design features. This embodiment illustrates a resonator 24that is not straight. Further, it illustrates the location of thepiezoelectric element 22 along an axis that does not intersect thedriven element. Moreover, it illustrates a different alignment andorientation of the piezoelectric element 22 and the resonator 24. Theaxes are inclined relative to each other, with the axis of piezoelectricelement 22 generally parallel with the axis 45 of the driven element 42.The axis 25 of the resonator 24 is inclined to bridge the gap betweenthe two axes 95, 45. The selected contacting surface 44 comprises acurved surface conforming the shape of the abutting contact area on therod-like driven element 42. The curved surface may be manufactured or itmay be generated by natural wear during operation of the motor. Theresilient mounting system accommodates motion of the selected contactsurface 44 that moves the rod 42.

Advantageously, the resilient mounting system comprises one or moresprings 50. In the illustrated embodiment, if the rod 42 is in ahorizontal plane, then a spring 50 a aligned in the horizontal planethrough piezoelectric axis 95 and perpendicular to (but offset from) thelongitudinal axis 45 provides the resilient mounting system.Advantageously, there are two springs 50 a extending on opposing sidesof the resonator 24 to provide a symmetric resilient mounting, althoughonly one spring 50 a could be used. The springs 50 a are shown connectedto the resonator 24 by interposing distal ends of the springs 50 abetween the piezoelectric element 22 and the opening 28 in resonator 24.Instead of separate springs 50 a, a single leaf spring element with itsmiddle abutting piezoelectric element 22 could be used.

Alternatively to spring 50 a, or in addition to spring 50 a, a spring 50b connects to the resonator 24 adjacent the end 35 in an axis orthogonalto the horizontal plane. Depending on the relative stiffness of thesprings 50 a, 50 b, and the relative location of those springs, variousmotions of the driven element 42 can be achieved. Preferably, the motionis a combined rotation about, and translation along axis 45, but a purerotation or a pure translation of the driven object 42 could also beachieved.

Suspension: A resilient mounting system 50, called the suspension, isconnected to the vibration element 26 to ensure that the selectedcontact portion 44 is consistently urged against the engaging portion ofthe driven element 42 so that the elliptic motion 100 of the contactportion 44 can transport the driven element 42. Similar principles applyif the driven element 42 is resiliently suspended and urged against thecontacting portion 44 instead. This consistent resilient force ispreferably maintained even if the driven element has a varying surfacesmoothness or configuration and if the contact portion 44 shows signs ofwear. For a small resilient force, these motors have been shown totransport the driven object 42 quickly, but provide small force. For alarger resilient force, the transportation speed decreases, but thetransportation force increases. If the resilient force is selected toolarge, the driven object typically stops.

Depending on the location of the selected contacting portion 44 and theconfiguration in which one or more vibratory elements 26 are arranged(e.g., FIGS. 23–42, different suspension systems will be needed. Avariety of suspension systems are illustrated in FIGS. 1, 2, 5 and17–22, and portions of the suspension system are discussed in thesection on Mounting Of Vibratory Elements & Driven Elements. Thesuspension system described here is primarily a spring-based suspensionsystem, but need not be so limited. The suspension could include leafsprings, coil springs and other types of springs; it could includeresilient materials such as elastomers or compressed gas springs, toname a few. The effect of the suspension system on the vibration modesof the vibratory element 26 will vary with the specific type ofsuspension system used and its arrangement.

For example, FIG. 74 shows a suspension system using a curved, flatspring 188 having a first end 188 a connected to base 52 and an opposingend 188 b connected to the vibratory element 26. In the depictedembodiment, the spring 188 is interposed between one end of thepiezoelectric element 22 and the adjacent wall, which defines an opening28. The vibratory element 26 is inclined at an angle α relative to theengaging surface of the driven object 42. The curved spring 188 offersthe possibility of providing a smaller motor assembly 20 because thecurved spring can reduce the needed space for the suspension. The wheel46 could contacts the driven element 42 using a flat edge of the wheelconcentric with the rotational axis 65, as illustrated in FIG. 74. Thewheels 46 could also have contoured peripheries configured to engagemating shapes on adjacent portions of the driven element 42 in order toappropriately support and guide the driven element 42. Given the presentdisclosure, a variety of movable support configurations will be apparentto those skilled in the art.

Another example is shown in FIG. 1 where the vibrating element 26 ismounted to and moves about the location where end 50 a is mounted tobase 52. The selected contact portion 44 is located relative to themounting of spring end 50 a to the base 52 so that a generally verticalaxis passes through both the mounting point 50 a and the contactingportion 44.

In contrast, the C-clamp configuration of FIG. 5 has the vibratingelement 76 rotating about pin 78. A vertical axes passing through thecontacting portion 44 is offset from a vertical axis passing through thepivot pin 78. The offset, combined with an asymmetric location of thepiezoelectric element 22, results in a different suspension system thatcan have different characteristics.

Portions of the resilient suspension system typically participate in thevibrations of the vibration element 26 and therefore affect thevibration modes. The design of the suspension system is advantageouslysuch that it enhances the desired motion of the selected contact portion44.

If a resilient suspension system, such as spring 50 is connected at anode of vibration at an operational frequency of the vibrator element26, then it does not participate in the vibration. But if the resilientsuspension system is connected at a location other than a node ofvibration at selected operating frequencies, then it creates anasymmetry that can couple various otherwise independent modes ofvibration of vibration element 26 together. This can result inelliptical motion 100 at the selected contacting portion 44 that isespecially useful if the engaging surface of the driven object 42 isinclined with respect to the vibration element 42.

For example, in the embodiment of FIG. 5, the vibration element 76oscillates about the pin 78, which can cause the contact portion 44 tohave an up-and-down motion along its elliptical path 100. The mountingof the vibrating element 46, 76 can result in a variety of vibrationmodes of the motor assembly 20 and various movement of the contactingportion 44.

Moreover, referring to FIG. 77 the further embodiment is shown that issuitable for use in a torsional motion or rotational motion of thedriven element. In this embodiment, the driven element 42 rotates aboutits longitudinal axis 45. The longitudinal axis 95 of the piezoelectricelement 22 is not aligned with the longitudinal axis 25 of the resonator24. The axes are inclined relative to each other, with the axis ofpiezoelectric element 22 generally parallel with the axis 45 of thedriven element 42. The axis 25 of the resonator 24 is inclined to bridgethe gap between the two axes 95, 45. The selected contacting surface 44comprises a curved surface conforming the shape of the abutting contactarea on the rod-like driven element 42. The resilient mounting systemaccommodates motion of the selected contact surface 44 that rotates therod 42 about its longitudinal axis 45.

Advantageously, the resilient mounting system comprises one or moresprings 50. In the illustrated embodiment, if the rod 42 is in ahorizontal plane, then a spring 50 a aligned in the horizontal planethrough piezoelectric axis 22 and perpendicular to (but offset from) thelongitudinal axis 45 allows the rotational motion of rod 42.Advantageously, there are two springs 50 a extending on opposing sidesof the resonator 24 to provide a symmetric resilient mounting, althoughonly one spring 50 a could be used. The springs 50 a are shown connectedto the resonator 24 by interposing distal ends of the springs 50 abetween the piezoelectric element 22 and the opening 28 in resonator 24.Instead of separate springs 50 a, a single leaf spring element with itsmiddle abutting piezoelectric element 22 could be used.

Advantageously, but optionally, a spring 50 b connects to the resonator24 adjacent the end 35 in an axis orthogonal to the horizontal plane.Depending on the relative stiffness of the springs 50 a, 50 b, and therelative location of those springs, various motions of the drivenelement 42 can be achieved. Preferably, the motion is predominantly orpurely rotation about longitudinal axis 45, although a combined rotationabout, and translation along axis 45 could also be achieved.

FIG. 77 also illustrates that the vibration element 26 and resonator 24can be non-symmetric. It also shows that the spring 50 can have variouslocations, configurations and orientations. Indeed, the spring 50 can bea bending or torsion spring, each of which can affect the suspension andresonant vibration modes of the system or of the vibratory element 26.FIG. 77 also shows that the spring 50 need not be connected to thepiezoelectric element 22. Moreover, the axis 25 of the predominantvibrating portion of resonator 24 need not be parallel to the axis 95through the piezoelectric. Further, the contacting portion 44 can bemolded to conform to the abutting surface of the driven element. Themolding can be preformed in the resonator 24, cut or otherwise formedinto the resonator 24, or it can be formed by wear and run-in.

A Mode of Operation to Reduce Friction:

It is an additional feature of the motors of this disclosure that whenexcited at certain frequencies, which are not the operationalfrequencies, they produce a varying contact force at the contact portion44, and possibly liftoff, which can reduce the effective frictionalholding force on the driven object 44. In other words, it is easier topull the driven object through the motor when operated at thosefrequencies, then when the motor is turned off. This property ofselectively reduced friction can be beneficial in certain applications.

Theoretical Design Aspects

The piezoelectric 22 and resonator 26 are configured to achieve adesired motion of the selected contact portion 44 that moves the drivenelement 42. The contact portion 44 preferably moves in an ellipticalpath 100 as shown in FIG. 1. Changes in phase and amplitudes of tworectangular components of motion of the resonator 26 and theirsuperposition to achieve that elliptical motion are described here(similar results can be derived for oblique angles). By modifying thephase and amplitudes several properties of the ellipse useful to thepresent application in motor assembly 20 are better understood. Theseproperties include the orientation and lengths of the short and longsemi-axes of the ellipse that is the path preferably traveled by theselected contact portion 44. Other relevant properties could alsoinclude the speed by which the ellipse is traversed, which correlates tothe speed of the contact portion 44 and thus the speed with which thedriven element 42 moves. The design may require the direction of thesemi-axis of the ellipse to be aligned with certain dimensionaltolerances within the piezoelectric motor assembly 20. The design mayalso require that the lengths of the semi-axes of the ellipse 100 do notexceed certain predefined limits. Moreover, the ratio of the semi-axesof the ellipse 100 can be advantageously selected to provide greatermotion, or faster movement, with the ratio of the axes advantageouslybeing 5:1, preferably 10:1, and ideally from about 10–50:1.

Referring to FIG. 43, the ellipse 100 represents the potential motion ofcontact portion 44 of the vibrating element 26 as shown in FIGS. 1 and5, among others. The ellipse 100 is generated by two components ofmotion, the first acting in the E_(x)-direction (which corresponds tomotion along the longitudinal axis 45 of the driven element 42 in FIG.1). The second component of motion acts in the E_(y)-direction, which isperpendicular to the E_(x)-direction. The two components of motionE_(x), E_(y) are generated at the selected contact portion 44 of themotor assembly 20. The mechanism used to generate the components ofmotion do not affect the following disclosure. Localized major and minoraxes e_(x), e_(y), respectively, of the ellipse 100 are also shown.

For illustration, the first and second components of motion E _(x),E_(y) are assumed to be sinusoidal with amplitudes A and B,respectively, and to have a phase difference of φ=π/2+Δφ[rad]. But otherwaveforms could be used. The position vector r of the selected contactportion 44 located at the edge of the resonator 24 as depicted in FIG.1, as a function of time, is:r=A cos(ωt+φ)E _(x) +B sin(ωt)E _(y).

In this equation, ω is the frequency of the oscillation. FIG. 44 showsan example of the partial components of motion for A=1, B=0.5, ω=1 andφ=π/6[rad]. The ellipse 100 of FIG. 43 is traversed counterclockwise for|Δφ|<90°, and clockwise for 90°<|Δφ|<270°.

The lengths 2 a and 2 b of the long and short semi-axes are thencomputed from, respectively:2a ² =A ² +B ²+√{square root over (A ⁴ +B ⁴−2A ² B ² cos(2Δφ))},2b ² =A ² +B ²−√{square root over (A ⁴ +B ⁴−2A ² B ² cos(2Δφ))}.

FIG. 45 depicts how b/B depends on Δφ and the ratio B/A. FIG. 46 depictsthe dependence of a/A. It is important to notice that the dependence ofb/B does not change substantially for ratios of B/A<=0.3. A goodapproximation of this dependence for |Δφ|<50° and B/A<=0.3 is given bythe function

$\frac{b}{B} = {1 - {\frac{\left( {\Delta\;{\varphi\mspace{14mu}\lbrack{rad}\rbrack}} \right)^{2}}{2}.}}$

The orientation angle α (FIG. 43) cannot exceed the value atan(B/A) (seeFIG. 47). As design rule, one has, for B/A<0.5

${{atan}\left( \frac{B}{A} \right)} \approx {\frac{B}{A}.}$

The angle α can for sufficiently small ratios B/A be approximated by(see FIG. 48):

${\tan(\alpha)} = {{- \frac{B}{A}}{{\sin\left( {\Delta\;\varphi} \right)}.}}$

The following example illustrates the usage of the previous material.Assuming that B/A=0.3. From FIG. 47 we find that atan(B/A)≅15°. Itfollows then from FIG. 48 that for Δφ=45°, α≅0.8*15°=12°. FIGS. 45–46indicate that b/B≅0.7 and a/A≅1.025.

This information illustrates how to change A, B and Δφ together in a waythat preserves or achieves various properties of the ellipse 100. In theprevious example, the changes can be made such that the angle ofinclination α (FIG. 1) between the longitudinal axis 25 of the vibratoryelement 26 remains close to 12 degrees in order to achieve a largetranslation of the driven element 42. The changes may also be made toensure that 2 b, the length of the minor axis of the ellipse 100 (FIGS.1, 43) remains larger than a given value in order to ensure thevibratory element 26 causes the selected contact portion 44 to disengagefrom the driven element 42 sufficiently to not only avoid undesiredmovement of the driven element 42, but to avoid unacceptable wear of thedriven element 42. Over a relatively wide parameter range a desiredellipse 100 can be achieved that is particularly useful for moving adriven element 42 in the present invention. In the example above, thedriven element 42 would be preferably oriented in an angle of 12 degreesto the E_(x)-direction. But it should apparent to one skilled in the artthat the optimal angle is in general not restricted to this value.

Referring to FIGS. 1, 43 and 49–51, it is also advantageous to considerthe influences of a coordinate transformation from the coordinate systemhaving an axis aligned with the longitudinal axis 25 of the vibratoryelement 26, to the coordinate system corresponding to the ellipticalmotion of the selected driving portion 44. This can illustrate usefulaffects on the frequency response curves and therefore on theperformance and design of the motor assembly 20. FIG. 43 illustrates themotor coordinate system defined by axes E_(x) and E_(y), where the E_(x)axis corresponds to the longitudinal axis 45 of the driven element 42(FIG. 1). The ellipse 100 is believed to be generated by a first and asecond motion component of the selected driving portion 44 on thevibratory element 26 of FIG. 1. The localized axes of the ellipse 100are represented by axes e_(x) and e_(y).

For example, we assume the first component of motion lies in theE_(x)-direction and has a transfer function that in the vicinity of aselected frequency can be approximated by a constant amplificationfactor g₁(s)=A. The second component of motion lies in theE_(y)-direction and has a transfer function that in the vicinity of aselected frequency can be approximated by a second order resonator givenby its Laplace transform:

${g_{2}(s)} = {\frac{k}{s^{2} + {2e\;\omega_{o}s} + \omega_{0}^{2}}.}$

Here ω₀ is the (undamped) resonance frequency, and e is a dimensionlessdamping parameter arising inherently from damping in the mechanicalsystem, i.e., the motor assembly 20 in this case.

The superposition of g₁(s) and g₂(s) yields transfer functions G₁(s) andG₂(s) in the e_(x) and e_(y) directions, respectively. For illustration,examples are given in which A=1 and ω₀=1. FIGS. 49–51 depict G₁(s) andG₂(S) for k=0.01 and α=25 degrees. The parameter e increases from FIG.49 to FIG. 50 to FIG. 51. The combination of these two signals resultsin a behavior where the phase difference Δφ between G₁ (s) and G₂(s)undergoes an intermittent change that becomes more rounded as thedamping in the system increases. This effect results in an expandedfrequency range where the relative phase difference lies between 0 and180 degrees, which makes it easier for a resonant frequency to be foundthat results in a useful, elliptically shaped motion. This frequencyrange is considerably wider than what would be achieved with thetransfer function of a simple second order oscillator. Such aparticularly widespread phase range can be used in conjunction withother design aspects to help select the shape and orientation of theresulting ellipse 100 as the selected driving frequency is changed.

The influence of the above coordinate transformation becomes moreinvolved as G₁(s) and G₂(s) are replaced by higher order, and morerealistic, transfer functions as they arise from the piezoelectric motorassembly 20. Such transfer functions can create relative phase shifts Δφbetween G₁(s) and G₂(s) that fluctuate between 0 and 180 degrees in evenwider frequency ranges, thus rendering the motor assembly 20 even lessdependent on production tolerances, material properties, temperaturevariations, and other manufacturing factors and criteria.

This phase shift between the longitudinal and lateral motion is used toachieve the desired elliptical motion. Phase shifts of between 3 and 177degrees are believed well suitable to achieve useful motion at theselected contacting portion 44. A 90 degree phase shift results in acircular motion if amplitudes are equal. Preferably, but optionally, thephase shift results in non-circular motion of the selected contactingportion 44 in order to obtain greater movement along the major axis ofthe elliptical motion.

The portion of the ellipse 100 below the E_(x) axis can be thought of asreflecting the engagement of the driving portion 44 with the drivenelement 42. By altering the shape of the ellipse 100 (i.e., 2 a, 2 bmeasured along e_(x) and e_(y)) the duration of the engagement can bevaried and to some extent the pressure of that engagement can be varied.Further, by altering the orientation of the ellipse 100 (i.e., the angleof inclination α between the axis 45 of the driven element and the majoraxis of the ellipse) the duration of the engagement can be varied. Asthe angle of inclination α comes closer to aligning the ex axis with theE_(x) axis, the duration of the contact between the driving portion 44and driven element 42 increases.

For practical reasons, the longitudinal axis of the driven element 42may often be placed between the two axes E_(x) and e_(x). But the moreimportant aspect is that these equations show that as the excitationfrequency of the piezoelectric 22 changes, the amplitude and phase ofthe selected driving portion 44 (i.e., ellipse 100) change. This showsthe ability to alter the amplitude and orientation of the ellipse 100and thus alter the characteristics of the motion driving the drivenelement 42. Moreover, the equations reflect an ability to offer thesevariations over a wide range of amplitudes and frequencies which offersa flexibility in functional design characteristics of the piezoelectric22 not previously available. Further, the equations reflect the abilityto vary the engagement criteria to a sufficient extent that themanufacturing tolerances can be less, and potentially significantly lessthan with many of the existing motors using piezoelectric drives.

Historically, these various manufacturing criteria have been so precisethat they result in costly manufacturing of piezoelectric vibratoryelements 26, and the motors have narrow operating ranges and criteria.Thus, the ability to use more liberal criteria offers the possibility ofsignificant cost savings in producing the motors while offering wideroperating parameters.

The direction of the motion of the driven element 42 depends on therelative orientation of the driven element 42 and the direction of theselection contacting portion 44 as it moves around its elliptical pathof travel 100. Different points of the vibration element 26 can showdifferent vibration shapes. Typically areas with clockwise andcounterclockwise motion around elliptical paths 100, alternate along thelength of the vibration element 26. The driving direction of a rodshaped vibration element 26 can typically be reversed by turning thevibration element by 180 degrees about longitudinal axis 25.

The shape of the motion of the contact point 44 is important to thisinvention. This shape must achieve more driving force in one directionthan in the other. This is typically achieved by increasing the contactpressure while the selected contact portion 44 moves in the directionthe driven element 42 gets moved. When the contact portion 44 moves inthe opposite direction the contact pressure is reduced or the contactingportion 44 even looses contact with the driven element 42. One importantaspect is how to generate the appropriate motion.

Because of mechanical noise and unwanted vibrations, the shape of theellipse does not always follow the ideal theoretical path. This mayresult in the selected contacting portion 44 sometimes performingmotions that are undesired, such as figure-eight shaped motion. Butthese motions may nonetheless regularly appear with the vibrator element26. They are, however, not used to drive the driven elements 42. This isclarified in the discussion of the three-dimensional vibration shapes ofthe contacting portion 44.

In the description only the two-dimensional shape of the vibration willbe addressed. In actuality the contacting portion 44 will have someslight motion in the third dimension, the direction perpendicular toboth directions of the driving force along axis 25 and the direction ofthe contact force between vibration element 26 and driven element 42which is generally along axis 45. These vibrations might also containhigher frequency components. As a result the motion of the contactportion 44 could look like a figure-eight motion if projected intocertain planes. Although this figure-eight motion can be observed, it isnot relevant for the operation of the vibratory element 26 driving thedriven element 42 and is merely a side effect of unused motion.

Ideally, the major axis of the elliptical motion 100 is perfectlyaligned with the direction in which the driven element 42 moves in orderto optimize performance. Perfect alignment is difficult to achieve formany reasons, including manufacturing tolerances and performancevariations. Further, even the elliptical path 100 is not perfectlyelliptical and may vary over time. Variations in voltage, current, powerdisruptions or fluctuations, degradation over time, electrical noise,mechanical noise, electromagnetic interference, to name a few, canaffect the shape and smoothness of the elliptical paths 100. Thus, it isdesirable to be able to configure a system that can accommodate apractical range of variations in order to reduce manufacturing costs andassembly costs, and to produce a system that can accommodateenvironmental variations and other variations that arise during use ofthe system. Because of such variations, an alignment of about 0–5degrees will be considered to be aligned, in part because in mostinstances this variation from perfect alignment does not substantiallyaffect the performance of the systems disclosed herein.

The vibrator element 26 does not rely on traveling waves for themovement of the selected contacting portion 44. But any mechanical waveexisting in material also travels through it. In the present inventionsuch waves get reflected at some part of the vibration element 26causing another traveling wave that superimposes with the first one.This results in a standing wave, and in some instances this standingwave can be used in connection with a selected contacting portion 44.Several prior art motors require a wave that is not standing, but rathertraveling—with the driven object moving with or being moved by thetraveling wave. The traveling wave is different from the standing wave.

Practical Design Aspects:

The contacting portion 44 is the point of the vibrating element 26 thatcomes in contact with the driven object 42 in order to move the drivenobject. That contacting portion is typically a portion of the resonator26, and is preferably on the distal end 36 of the resonator. The powerof the motor assembly 20 to move heavier driven elements 42 and theefficiency of the motor assembly 20 are functions of the periodic motionof the contacting portion 44 and of the force between the contactingportion 44 and the driven element 42.

The spatial motion of the selected contacting portion 44 is the resultof the superposition of several vibration modes of the motor. Thesemodes are all excited, to varying amplitudes and relative phases, at thesame frequency generated by the piezoelectric element 22. Theircontributions to the desired motion of contacting portion 44 and forcesapplied by contacting portion 44 are a function of the relativemagnitudes and the relative phase angles of each of these severalvibration modes. These vibration modes in turn are functions of themotor geometry, constitutive relations, and the material properties.

In order to increase the performance of the motor assembly 20, thefollowing guidelines may be used. Preferably all of the followingguidelines are simultaneously satisfied at the selected contact portion44 in order to optimize the performance of the motor assembly 20, butcompromises of one or more of these guidelines can occur if theresulting motor performs satisfactorily.

The motion of the selected contacting portion 44 is elliptical withmajor and minor axes of lengths a and b, respectively. As used here, andunless specified otherwise, the reference to elliptical motion or to anellipse includes ellipses with the major and minor axes are equal, whichforms a circle. The reference to elliptical motion or to an ellipse alsoincludes ellipses in which either of the major or minor axes are smallrelative to the other axis, which results in a very elongated ellipseapproaching a straight line.

The major axis of the ellipse is preferably aligned with the drivingdirection of the driven element 42. The length of the major and minoraxes, a and b, are both large enough to achieve their desired uses, andpreferably large enough to provide optimum performance for the selectedapplication. The generally preferred elliptical shape has an elongatedmajor axis “a” relative to the minor axis “b” in order to increasespeed, and has a minor axis “a” sufficient to disengage the contactingportion 44 from the driven member 42 during the return portion of theellipse, as discussed next. As discussed above, ratios of about 3:1 upto 150:1 or even greater are believed usable, although the higherratio's provide more linear motion and result in more impact motion withthe driven element.

The force at the selected contact portion 44 normal to the contactsurface on driven element 42 is large when the contacting portion 44moves in the driving direction, and small (or zero), when the contactportion 44 moves against it. If the force is zero, the contactingportion 44 has lost contact with the driven object 42. In thatlost-contact case, the backward motion of the vibratory element 26 tipis very efficient, but the motor assembly 20 also loses traction duringthat period of time. This loss of traction should be considered whenevaluating motor efficiency and strength. If the normal force is toolarge when the contact portion 44 moves against the driving direction,the driven element may not be properly transported in the drivingdirection, which results in a loss of performance.

Moreover, the normal contact force between the selected contactingportion 44 and the driven element 42 is a measure of the friction forcebetween the contacting portion 44 and the driven object 42. Largernormal forces provide the motor assembly 20 with stronger thrust. Butthe wear occurring over the repeated contact from the many thousands ofcycles of elliptical travel must also be considered. Larger contactareas on the contacting portion 44 have the advantage of tolerating moredefects in the surface of the driven element 42 that engages thecontacting portion 44.

In the embodiments thus far disclosed, the selected contacting portion44 is often illustrated as being located on one edge of the distal end36 of the vibration element 26, in part because the desired ellipticalmotion can be readily achieved at that location. Moreover, the edgelocation provides a narrow area of contact and good frictionalengagement. But it is not necessary that the selected contacting portionhas to be located on an edge. Moreover, typically some material wearwill wear out the edge and provide a flat or flattened contact surface44 after some period of use. This wear typically does not affect theoperation or use of the motor assembly 20. As discussed elsewhere, thecontact portion 44 can also be located at other places on the vibrationelement 26. For example, the contact portion 44 could be located on theside of the vibration element 26 as in FIG. 62. The selected contactingportion 44 does not have to be a point contact. The particularapplications will thus influence the size and location of the selectedcontacting portions 44.

The displacement of the contacting portion 44 in the driving directionand the normal contact force are not in phase. These two quantities forman ellipse when plotted in a displacement/force diagram. The orientationof the major axis of this ellipse with respect to the displacement axisprovides another design parameter. Depending on this orientation, themaximal contact force is generated earlier or later during the forwardmotion of the tip. In a certain sense this could be interpreted assomewhat analogous to a saw-tooth-like movement. Because useful motioncan be achieved when one semi-elliptical axis of the elliptical path 100is about 5, 10 or more times greater than each other axis, evenrelatively small motions can be of potential use for one of thesemi-axes.

The motion of the selected contacting portion 44 is the result of thevibrations of the entire motor assembly 20 and its components. Largemotions of the selected contacting portion 44 are achieved if theexcitation frequency lies close to a resonance frequency of the system,and if the selected contacting portion 44 is located where a largeamplitude occurs. In order for the motion of the selected contactingportion 44 to be multi-directionally large, the motor assembly 20 isadvantageously designed to have several resonance vibrations clusteredin a selected frequency range. For example, if the natural frequency ofa bending mode is close to that of a longitudinal mode, and theexcitation frequency lies in between the frequencies that excite thesebending and longitudinal modes, then the resulting motion of theselected contacting portion 44 will have moderately large amplitudes.The elliptical nature of the motion of the selected contacting portion44 is generated by the phase difference of the respective motions. Thephase difference is generated in part by the damping in the system.Various combinations of these factors can be used to achieve the desiredmotion of contacting portion 44 and to achieve other criteria of themotor assembly 20, such as power, reliability, wear, etc.

The absolute and relative locations of the resonance frequencies andvibration modes of the motor assembly 20 are affected by a multitude ofparameters. The following factors can be used to configure an acceptabledesign of the motor assembly 20.

Lower vibration modes are generally stronger than higher vibration modesbecause the lower vibration modes store relatively less elastic energy,leaving more energy for driving the object 42 through the selectedcontacting portion 44.

The location of the longitudinal resonance of the vibrating element 26in a frequency diagram is affected mainly by the length of thepiezoelectric 22 and resonator 24 and by the material properties of theparts. The first longitudinal mode is by far the strongest and thereforethe more desirable mode to use.

The location of the longitudinal resonance of the vibratory element 26in a frequency diagram can further be affected by the motor suspension,i.e., by the spring steel support 50 (FIG. 1) or other mechanisms thatconnect the vibratory element 26 to its housing. If a natural(resonance) frequency of the support such as spring 50 is brought closeto the longitudinal resonance frequency of the vibratory element 26, ithas the effect of splitting the longitudinal frequency into twofrequencies which are close to each other. The phases of the modesfluctuate strongly between 0 and 180 degrees in these resonance areas.Resonance splitting can therefore be used to spread the working regionof a motor over a wider frequency range, making the motor therefore morerobust.

Phase differences other than 0 and 180 degrees are induced by dampingmechanisms. In order to expand this effect over wider frequency areas,additional damping elements such as damping layers can be added to thevibratory element 26, or to various portions of the motor assembly 20.Also, internal damping is affected by the material properties of thepiezoelectric 22 and resonator 24 and by the way in which they areassembled. These factors in turn can be affected by the material'shistory, i.e., its manufacturing process.

Moreover, whether the damping is inherent in the system materials oradded by design components, the damping can be used so that a primaryresonance mode is used to excite a secondary vibrational mode thatresults in the desired elliptical motion of a selected contactingportion 44 along path 100. Recall that the elliptical semi-axes can haveamplitude ratios of 5, 10 or more, such that a vibration mode excited bydamping need only have an amplitude of ⅕, 1/10 or so of the amplituderesulting from the primary vibrational mode. Because damping can couplevibration modes, the damping can be used to achieve the desiredelliptical motion of the selected contacting portion.

Bending resonance vibration modes are affected mainly by the length andcross-sectional areas and shapes of the piezoelectric 22 and resonator24 and also by the material properties of those parts. Lower resonancevibration modes are stronger than higher ones. Guidelines for placingand splitting of resonance longitudinal vibration modes also apply tobending modes.

Shearing resonance vibration modes can contribute to the longitudinalmotion of the selected contacting portion 44, especially if thecontacting portion 44 is located at a distal end 36 of the vibratoryelement 26 and on an edge of the distal end. The shape of thecross-sections of the resonator 24 affects these resonance vibrationmodes, as does the placement of the piezoelectric 22 relative to theresonator 24. Further, as an example, see FIG. 2. If the longitudinalaxis of the piezoelectric 22 is appropriately offset from thelongitudinal axis of the resonator 24, an edge of the distal end 36 canhave a shearing resonance that causes opposing edges at distal end 36 topivot about axis 40. Removing material close to the centerline of themotor can have an especially strong effect on this resonance mode. Oneconfiguration with material removed along the centerline is shown inFIG. 52, and described later.

Torsion resonance vibration modes can be used to support selected, andpreferably vertical motion of the selected contact portion 44 if theportion 44 is close to a side of the vibratory element 26. The torsionresonant vibration modes are usually of smaller magnitude than othervibration modes, but they offer the possibility of using variousportions along the length of the vibratory element 26 to drive variousobjects. Torsion resonant vibration modes could be used to rotate thedriven element 42 in the embodiments of FIGS. 23, 25, 27, 28, 29, 30, 32and others. Torsion resonant vibration modes could be used to translatethe driven element 42 in the embodiments of FIGS. 38–40.

Resonant vibration modes arising from cross-sectional contraction are oflittle benefit when the driven element is elongated, such as therod-like driven element 42 depicted in FIG. 1. The cross-sectionalcontractions appear at frequencies that are too high to produce readilyusable amplitudes. Cross-sectional contraction is governed by thePoisson-effect. This effect is strongest where the longitudinal strainsin the piezoelectric element 22 or resonator 24 motors are the highest,i.e., where the stresses are highest. Cross-sectional contraction cantherefore be large where the piezoelectric element 22 is connected tothe resonator or whatever frame is holding the piezoelectric element andthe portion of that connection in which the forces are high. Thiscontraction can drive the bending vibrations of the thin sidewalls 29(FIG. 1) of the resonator 24. If the bending resonant vibration modes ofthe sidewalls 29 are tuned to the longitudinal vibration mode of thevibratory element 26, yet another splitting of natural vibrationfrequencies can occur with similar benefits as mentioned above.

The piezoelectric element 22 generates predominantly longitudinal forcesin the resonator 24 within which it is mounted. Coupling of theselongitudinal forces from the vibratory element 26 into directions otherthan along longitudinal axis 25 creates a number of other possiblevibration modes within the vibration element 26, such as bending, shearand torsion. The intensity of the coupling of the longitudinal motionwith other vibratory motions within the vibratory element 26 candetermine the relative amplitudes of the various modes of the vibratoryelement 26 and therefore their relative contributions to the motion ofthe selected contact portion 44. Coupling can be generated by materialproperties, geometric imperfections and asymmetries within thecomponents of the vibratory element 26, primarily the piezoelectric 22and the resonator 24.

Some of these coupling effects are often poorly defined, difficult toanalyze, and hard to measure or design. Well-defined mechanisms aretherefore preferable. These mechanisms include mounting thepiezoelectric element 22 off-center of the longitudinal axis 25, or atan angle to the longitudinal axis 25 of the vibratory element 26, orusing flexible mountings for the vibratory element 26 such as a spring50 or similar elements. In the case of a spring 50, the longitudinalmotion of the vibratory element 26 generates bending in the spring 50.The end 50 b of the spring that is clamped to the vibratory element 26is forced to bend or possibly to twist. This bending or twisting causesbending moments to be generated in the vibrational element 26. Theconfiguration of the spring 40 could be used to vary the vibrationalmode, as for example by introducing bends, edges and similarmodifications into a flat metal spring. Furthermore, the spring 50 canbe made more flexible at specified locations to better define an axis ofrotation about the flexible portion, if that is useful to the design.Coupling of vibration modes within the vibratory element 26 can also beachieved if the piezoelectric element 26 is selected or configured orexcited to perform other than pure longitudinal motions.

Several additional factors are preferably considered in configuring thevibratory element 26 and the motor 22. These factors include: theorientation of ellipse 100 in which the selected contact portion 44moves when it is not in contact with anything; the orientation of theforce-displacement ellipse of the contact portion 44 when it is incontact with the driven element 42; and an estimate of mechanical powergenerated at the selected contact portion 44 when it is in contact withthe driven element 42.

Reversing Direction

If a principle of operation of the vibration element 26 is known totransport the driven object 42 in one direction at a first frequency, itis desirable to use the same principle of operation at a secondfrequency to transport the driven object in the opposite direction. Sucha design is not only useful for vibration elements that operate usingelliptical motion, but also for vibration elements that operate on otherprinciples. The vibration modes of the vibration element 26 that producethe transporting motion in the contacting portion 44 at the firstfrequency are not necessarily the same as those that produce thetransporting motion at the second frequency, nor are they necessarily ofthe same type.

It is an advantage of such a multi-directional design that—provided thevibration element 26 is appropriately designed—the same mechanicalcomponents that are necessary to achieve unidirectional movement can beused to achieve bi-directional movement at two distinct operationalfrequencies. In particular, a single vibration source 20, e.g., apiezoelectric element, is sufficient.

The realization of a multi-directional design is simplified if the axis25 of vibration element 26 is oblique to the direction of transport ofdriven element 42. Also, in many cases the shape of the motion of thecontacting portion 44 at either operational frequency may not be optimalto achieve maximal force or speed of transport, but only a compromise toachieve suitable bi-directional performance. Furthermore, the frequencyrange within which the vibration element transports in one direction isnot necessarily as large as the range within which it transports in theother. Testing has shown that a frequency range of 5 kHz at a firstfrequency and at least 300 Hz at the second frequency are possible tomove or transport a driven element in opposing directions.

Illustrative Designs

Various modifications on the design of the resonator 24 holding thepiezoelectric element 22 are possible to enhance the performance of thevibratory element 22. The following implementations are somepossibilities. Combinations of these following embodiments, and of theprior embodiments, are possible. All combinations of methods forclamping the piezoelectric element 22 and of the various mountingmethods are also believed possible.

FIGS. 52–55 show a vibratory element 26 having a resonator 24 with aslot 112 extending from adjacent the cavity 28 to adjacent the distalend 36, and extending through the resonator, along the direction oflongitudinal axis 25. The slot 112 preferably has rounded ends andparallel sides. But the slot could have rectangular shaped ends. Thereare advantages to using longer, narrower 112 compared to wide slots asshown in FIG. 54. The narrower slots 112 result in beams 114 with largerdimensions, so that manufacturing tolerances have less effect on theresulting vibration. If the slots 112 are large, the walls 114 areusually smaller in dimension so that errors in manufacturing have alarger effect on the vibrational performance.

The slot 112 preferably opens onto the same surfaces of the resonator 24as does the opening 28. But this need not be so, as the slot could openonto other surfaces of the resonator 24 depending on the vibrationalmodes and configurations that are desired. FIG. 55 shows the slot 112opening onto a lateral surface turned 180 degrees from the orientationof the opening 28. Various angular orientations are possible, especiallyif the resonator 24 has a cylindrical body shape. The slot 112 creates aresonator with two beam segments 114 a, 114 b, on opposing sides of theslot, each of which forms a portion of resonator 24.

In FIGS. 52–54, the slot 112 is illustrated as fairly symmetricallylocated in order to produce side-beams 114 of approximately equaldimension with close vibrational modes and frequencies. But the slot 112need not be symmetrically located as reflected in FIG. 55, and can belocated to produce beams 114 a, 114 b of very different dimension andwith different resonance frequencies. Moreover, more than one slot 112can be used.

The slot 112 in the resonator 24 can thus create an increased number ofbeams 114 in the resonator, with each beam vibrating at its owneigenfrequencies and selected for that very reason. The increasedeigenfrequencies leads to an increased number of phase shifts of thevibrations in the resonator 24. By having two almost identical beams 114a, 114 b with eigenfrequencies very close together, it is also possibleto get a wider frequency range with high amplitudes.

The slot 112 also changes the mass distribution of the resonator, thebending of the resonator, and the shear stiffness of the resonator 24.Each of these changes has an influence on the resonant frequencies andresonant vibration modes of the resonator 24 and of the vibratoryelement 26. This gives a flexibility of design that allows a broaderrange of frequencies to excite the requisite vibration modes ofvibratory element 26 while allowing lower manufacturing tolerances.

In FIG. 53, the opening 28 for the piezoelectric element 22 has roundedends rather than flat ends over the portion that abuts the piezoelectricelement 22. The contact area between piezoelectric element 22 and theend of the opening 28 comprises two lines when the piezoelectric elementhas a square or rectangular cross-sectional area. This can provide amore defined contact. If the opening 28 is formed by a wall abutting thepiezoelectric element 22, the wall is typically not perfectly flat andnot perfectly orthogonal to the longitudinal axis 25. Moreover, the endof the piezoelectric element 22 is not perfectly flat and not perfectlyorthogonal to the centerline (e.g., longitudinal axis 25). Thus, whenthe end of the piezoelectric element 22 abuts the walls (e.g., end walls31) defining the opening 28, it is possible that the piezoelectric willnot be compressed along its centerline, with the result that thepiezoelectric will be compressed along an offset axis or a skewed axis.The offset axis or skew axis can result in a variation of vibrationalmodes. Alternative ways of resolving this contact location are discussedrelative to FIGS. 9–16.

FIG. 56 shows an embodiment with two slots, on each side of the opening28, along the piezoelectric element 122. The slots 112 open into theopening 28 to form an “H” shaped configuration with the piezoelectricelement 122 mounted at the center of the “H”. This configuration makesit easier to press-fit the piezoelectric element 122 into the resonator24 since the sidewalls 29 can take more deformation before neckingbegins.

FIG. 57 shows an embodiment in which the opening 28 is formed in one leg114 defined by centrally located slot 112, resulting in the leg 114 abeing divided for a portion of its length into further legs 114 c.Configurations such as this can have a high shear contribution to themotion at the selected contacting portion 44, which is illustrated asbeing aligned along the axis of leg 114 a. A different selectedcontacting portion 44 b on leg 114 b could be used to drive a differentelement at a frequency other than that used to activate the driving modeof leg 114 a. A third potential contacting portion 44 c on the leg 114could represent yet another frequency to yet another driven element whenactivated. This is another illustration that the selected contactingportion 44 need not always be at the same location on the vibratoryelement 26, as it will depend on a variety of factors, including thenumber, configuration and arrangement of the vibratory element(s) 26 andthe configuration of the driven element or elements motor assembly 20.

FIG. 58 shows an embodiment having a hole 116 in the resonator 24. Thehole is shown extending along the longitudinal axis 25 of the vibratoryelement 26, but it could be located off-axis, or skewed relative to thataxis 25. The hole 116 is shown as opening onto the distal end 36, but itcould be formed on any of the surfaces of the resonator 26. The hole 116is preferably cylindrical and results from drilling of the hole as closetolerances can be maintained at low cost with such holes. But othershapes could be used, as a drilled hole can be broached to achievevarious cross-sectional shapes. The diameter of the hole 116 can varydepending on the desired effect, as the hole changes the massdistribution by removing material, and it changes the stiffness of thematerial remaining after the hole is formed.

FIG. 59 shows an embodiment with a larger mass behind the piezoelectricelement 122, located between the piezoelectric element 122 and theproximal end 35 of the resonator 24 that is opposite the distal end 36.This extra mass enhances the vibration of the distal end 36 of thevibratory element 26 and is useful when the selected contacting portion44 is on the distal end 36.

FIG. 60 illustrates an embodiment with multiple sidewalls 29. It ispossible to not only have solid sidewalls 29 next to the piezoelectricelement 22, but it is also have a more complex sidewall configurations.

FIG. 61 shows a further embodiment in which the piezoelectric issubstantially enclosed and surrounded by the frame. This configurationis akin to inserting batteries into a flashlight. The opening 28comprises a close-ended hole, with the end 120 of the hole having eithera conical shape or a flat shape depending on the drill used to createthe hole. A cap 122 threadingly engages corresponding threads on the endof the hole 28 to compress the piezoelectric element 22 placed in thehole. The cap 122 is shown as having a curved end 124 to abut the cap 34on the abutting end of piezoelectric element 22 and create a pointcontact. Preferably, one or more small holes 126 are formed in thesidewalls 29 defining the opening 28 so that the electrical wires 30 canbe connected to the piezoelectric element 22. But other ways ofproviding electrical connections can be devised. The end 120 againstwhich the piezoelectric element 22 abuts forms an area contact if thebottom 120 is flat; it forms a four point contact if the cross-sectionof the piezoelectric or any protective cap 34 (not show) is square; andit forms a line contact if the cross sectional area of the piezoelectricor any protective cap 34 (not shown) is round.

Preferably the resonator 24 is machined or cast of non-ferrous metal,preferably aluminum. The resonator could be sintered of appropriatematerials. Moreover, it is believed possible that the resonator couldcomprise two separate sections joined by an appropriate adhesive toopposing sides of the piezoelectric element 22. Further, the resonator24 could be formed of a suitable ceramic material. If formed of aceramic material that is sintered, the resonator could be sintereddirectly to the piezoelectric during the sintering of the resonator 24.

Suspension of the Driven Element: The driven element 42 is preferablysuspended so that it can move relative to the vibratory element 26 andsupport or move a desired load. Usually the load is moved by pressing aportion of the driven element 42 against the load, as for example afiberglass rod connected to a CD tray that is moved reciprocally in andout of a housing by a linear motor assembly 20. But in some situationsthe driven element 42 itself may be the desired load. The driven element42 can be suspended on bearings. Less expensive methods are to suspendthe driven element on small wheels, or to use bushings as linearbearings. The bushings are believed to work well with rod-like drivenelements 42. A low friction and stiction coefficient between thebushings and a glass or fiberglass rod reduces the performance loss ofthe motor assembly 20 due to friction. Self-lubricating bearings aredesirable to further reduce friction losses. Other methods are possible.Other driven objects like a wheel or a ball also easily be suspended onan axle.

When the driven element 42 comprises a rod, it can also be suspended onat least four balls such that the rod can move linearly. The stiction ofsuch a mounting using four Delrin balls is believed to be less than withfour ball bearings. The balls preferably need to run in grooves in orderto transfer radial loads applied to the balls by the rod. Thus, the rodcould be grooved to provide a driven element 42 with longitudinalgrooves in it when the configuration of the motor assembly 20 isarranged to translate the rod. The orientation of the grooves wouldchange depending on the desired movement of the rod or driven element42. Further, the length of the grooves could limit the motion of therod.

A plate driven by the vibratory element 26 could also be suspended on atleast three balls. This would give the motion of the plate three degreesof freedom. Other methods are possible.

The driven element 42 could be suspended in a manner that resilientlyurges it against the selected contacting portion 44, using principlesdiscussed above for mounting the vibratory element 26. One resilientsupport is discussed regarding FIG. 6 above.

Electronics

A number of different electronic circuits can be used to drive thepiezoelectric element 22 of vibratory element 26 since the motor 26 isfunctional with a variety of different signal shapes applied to thepiezoelectric element 22, as long as the power spectrum of the inputsignal provides a substantial amount of vibratory energy at the desireddriving frequency sufficient to achieve the desired motion of theselected contacting portion 44. This ability is an advantage over thoseprior art motors that require specialized, more expensive electronics togenerate special waveforms, such as, for example, saw-tooth waveforms.Some specific examples of driver circuits are shown in FIGS. 63 to 66.

FIG. 63 shows an example of a driver circuit, preferably using ahalfbridge 152 such as a NDS8858H halfbridge available from FairchildSemiconductor. A discrete halfbridge is also believed suitable, but isnot as preferred for size reasons. A rectangular input timer-signal 150of specified frequency can be used to repeatedly switch between theinputs of the integrated halfbridge 152. This process generates anoscillatory waveform in the capacitor 154, which represents thepiezoelectric element 22. It is however not necessary for the signal 150to be rectangular as long as it reaches the necessary thresholds thatcan switch the halfbridge 152. The signal 150 can thus be generated by amicrocontroller, or by other suitable signal generators such as a LM555timer circuit available from National Semiconductor. The inputtimer-signal 150 is used to switch between the inputs of the halfbridge153. The period during which one of the said inputs is connected to theoutput of the halfbridge is determined by the input signal 150 and canbe appropriately chosen. Typically, the cycle during which the supplyvoltage (VCC) is connected through to the output of the halfbridgeaccounts for about 50% or less of the time in order to achieve the bestenergy efficiency in the circuit and in the piezoelectric element 22. Ifthe signal 150 is high, the n-channel transistor 153 a in the halfbridge152 becomes conductive and discharges the capacitor 154. After thisdischarge, it is preferable for the signal 150 to change to a lowerlevel so that the p-channel transistor 153 b in the halfbridge becomesconductive instead and charges the capacitor 154. This process can berepeated indefinitely and, since the capacitor 154 represents thepiezoelectric element 22, it results in a vibratory motion of thepiezoelectric element 22 and therefore of the vibratory element 26 (FIG.1).

As an alternative, one of the transistors 153 a, 153 b in the drivercircuit can be replaced with a component 156, e.g. a passive componentlike a resistor, or an active component such as a constant currentdiode. Such an alternative embodiment is shown in FIG. 64, where thetransistor 153 b has been replaced with a component 156 such as aresistor.

In accordance with specific embodiments, the driver circuits of FIGS.63, 64 have the advantage that they can be implemented within anintegrated circuit, e.g. as part of a microcontroller.

FIG. 65 shows an alternative driver circuit for the piezoelectricelement 22 that uses a switched resonance circuit having a capacitor 154(piezoelectric element 22), an electromagnetic storage device, such asinductive coil 158, and optional resistor 156 connected in parallel. Oneadvantage of using a resonance circuit to drive the piezoelectricelement 22 is the ability to lower the supply voltage (VCC) to batterylevel (e.g. 3V) while maintaining the higher voltages necessary tooperate the piezoelectric element 22. Moreover, the entire circuitconsists of only three electronic parts besides the capacitor 154, whichrepresents the piezoelectric element 22.

In FIG. 65, an input signal 150 (like the one previously described inthe halfbridge driver circuit of FIG. 63) is used to switch a controlelement 153, such as transistor, on and off in a well-determinedfashion. Typically the cycle during which the transistor 153 isconductive is chosen to be about 50% or less in order to achieve thebest energy efficiency in the piezoelectric element 22. When the inputsignal 150 is high, the transistor 153 becomes conductive and reversesthe charge of the capacitor 154 while increasing the current through thecoil 158. The current in the coil 158 reaches its maximum when thecapacitor 154 is fully charged. At that point in time, the coil 158stores a maximal amount of energy in its electromagnetic field, and itis preferable if the input signal 150 is set to low so that thetransistor 153 is no longer conductive. The energy stored in the coil158 sustains the flow of current, which in turn reverses the charge ofthe capacitor 154 resulting in an increased voltage across the capacitor154 and therefore the piezoelectric element 22.

When the capacitor 154 has fully reversed its charge and if the circuitadjustments are correct, the energy in the coil 158 increases thevoltage across the capacitor 154 beyond the supply voltage (VCC). Whenthe coil 158 has relinquished its energy, the voltage across thecapacitor 154 reaches a maximum, and the capacitor 154 now stores theentire electric energy of the system. Next, the current flow through thecoil 158 reverses which in turn causes another reversal of the capacitorcharge. At this point or shortly thereafter, it is preferable if theinput signal 150 is switched to high again so that the cycle can berepeated.

The resistor 156 is not necessary for the operation of the circuit ofFIG. 65, but it provides a method to shape the waveform at the capacitor154 and to cut off possible voltage peaks that can originate from thefast switching of the current through the transistor 153, hence reducingpotential electromagnetic interference as well as leakage of vibratoryenergy into undesired frequency spectra. Alternatively, the resistor canalso be put in series with the inductor 158. As a further alternative,it can be beneficial to place the inductive coil 158 in series with thecapacitor 154 to form another type of electric resonance circuit. If theresonance frequency of this circuit is chosen sufficiently close to anoperation frequency of the motor, higher voltages at the piezoelectricelement 22 can be achieved while maintaining relatively low electricpower consumption. As mentioned earlier, the inductor 158 canadvantageously also be a wire coil made from the same wire that connectsthe capacitor 154.

Further, referring to FIGS. 78–80, it is possible to integrate the coil158, and even the resistor 156, directly into the vibratory element 26by, for example, wrapping an insulated wire around the vibratory element26 to form an inductive coil as shown in FIG. 78. In such an embodiment,the two ends of the wire coil 158 can concurrently be used as electricalleads to the piezoelectric element, as shown in FIG. 79. The wire coil158 can be wound around the resonator 24 as in FIG. 30, or separate asin FIG. 80. These configuration place inductive coil 158 in parallel tothe capacitor 154 and save additional wiring, although the coil 185could be placed in series, with or without the damping resistors,half-bridge or single transistors.

Moreover, the inductive coil 158 can be mounted close to thepiezoelectric element 22 with which it can form the electric resonatorcircuit. The physical proximity of the piezoelectric element 22 and coil158 can reduce the inherent electrical resistance in the electricalconnections of those parts and can make the circuit more effective,especially since most of the current used to drive the motor oscillatesin this electric resonator. As a result, the wires leading from theelectric resonator consisting of the coil 158 and piezoelectric element22 to the signal generating unit can be reduced in diameter andincreased in length and may result in lower electrical interference.

A source of electrical signals, such as a signal generator, iselectrically connected to the vibratory element 26, and the source ofvibratory motion, 22, through various ways, e.g., a pair of wires 30. Inorder to move the driven object 42 in a first direction, the signalgenerator produces an electrical signal with a spectrum whose dominantfrequency is the corresponding operating frequency. Typical and usablesignals include, but are not restricted to, pure sinusoidal, triangularand rectangular waveforms. Similarly, a signal with a spectrum whosedominant frequency is a second or third operating frequency, can causethe driven object 42 to move in a second or third direction.

The capability of the various vibratory motors described herein toreliably operate with a variety of waveforms is an advantage over thoseprior art motors that require special waveforms other than sinusoidalwaves to function, e.g., saw-tooth waveforms, and that would notfunction reliably with a purely sinusoidal waveform. Therefore, sincethe quality of the signal applied to the piezoelectric element 22 can beless than compared to some prior art motors, the signal generator canhave a simpler construction, which results in a reduced cost of theentire motor system.

Furthermore, it is desirable to have all electrical signals produced bythe signal generator communicated through the same set of electricalconnections to the vibratory element 26, and particularly to thepiezoelectric element 22, e.g., by wires 30. When all signals arecommunicated through the same electrical connections, there is no needfor a unit that switches between various selected connections. Thisfurther simplifies the vibratory motor compared to prior art motors.Further, some prior art devices generate a phase shift between twoelectrical signals and then communicate the signals individually throughseparate electric connectors to at least one piezoelectric element, andthe present, more simplified electrical connection can avoid that morecomplex design. This can further reduce the cost of the motor incomparison to some prior art motors.

As illustrated in FIGS. 78–80, the piezoelectric element 22 can be sizedto extend beyond the portions that engage the walls forming the opening28. Thus, the piezoelectric element 22 is shown as extending beyond theend walls 31. This variation in the dimensions of the piezoelectricelement can be used to vary the value of capacitor 154, and thus theperformance of the control circuits, such as the circuit depicted inFIG. 65.

One potential disadvantage of the driver circuit of FIGS. 65 and 78–80is due to negative voltages that can appear across the capacitor 154.Negative voltages can be damaging to the piezoelectric element 22, whichis a polarized electrical component. In order to amend the situation forpiezoelectric elements susceptible to negative voltages, a modificationof the circuit can be provided as discussed relative to FIG. 66.

FIG. 66 shows a driver circuit suitable for use with a piezoelectricelement 22 that may be more sensitive to a negative voltage. In thiscircuit, a second physical capacitor 154 b is added to the piezoelectricelement 22 (represented as capacitor 154 a), or multiplayerpiezoelectric element 22, if it has multiple piezoelectric layers thatare electrically split as shown, can be represented as two capacitors154 a and 154 b. Also, another resistor 156 b is included in the circuitin addition to the existing resistor 156 a. Parallel to the resistors156 and the capacitors 154, two diodes 160 a, 160 b are added.

The orientation of the diode 156 a prevents the voltage of the nodebetween the two resistors 156 a, 156 b from falling below the supplyvoltage (VCC). The voltage across the capacitor 154 a therefore cannotbecome more negative than the typical voltage drop across a conductivediode (about 0.5–0.7 Volts). This small negative voltage can besustained by most piezoelectric elements.

If, in the same manner as before, the circuit is excited by the inputsignal 150 to resonate, the amplitude of the oscillating voltage acrossthe piezoelectric element 22 (represented by capacitor 154 a) can bemade larger than the supply voltage (VCC), but the voltage cannot becomenegative. A similar statement holds true for the physical capacitor 154b so that a polar electrical component may be chosen there as well.Further, if the piezoelectric element has multiple piezoelectric layersand is electrically split so as to be represented as two capacitors 154a and 154 b, the driver circuit of FIG. 66 advantageously requires onlya single control signal 150 to drive the piezoelectric element.

It has been observed that for a given voltage amplitude of the electricinput signal to the piezoelectric element 22, the electrical currentconsumption of the piezoelectric element increases sharply forexcitation frequencies just below certain resonance frequencies of thevibration element 26, and drops sharply just above those resonancefrequencies. For rod-like vibration elements 26, these frequenciestypically correspond to longitudinal modes. This electrical effect canbe used to cheaply and quickly determine a particular vibration modewithout using specialized measuring equipment such as a laservibrometer. The sharp decrease in current just above a certain resonancefrequency can be used to reduce the electrical power necessary to drivethe vibratory unit 26 if the motor assembly 20 can be operated at thesefrequencies. Also, the electronics could be configured to automaticallydetect the drop in current and track the frequency at which the dropoccurs, hence advantageously providing feedback. This feedback can beused to adapt the optimal operating frequency to changing externalinfluences, such as temperature and humidity. Also, this kind offeedback can be used to detect the mechanical load that the motor mustmove.

Specially Configured Piezoelectric Elements

In some embodiments where the piezoelectric element 22 is press-fit intothe opening 28 in the resonator, the walls defining the opening 28deform elastically and/or plastically during the press-fit process inorder to accept the larger piezoelectric element 22 and generate thepreload. One way to prevent the piezoelectric from experiencing sheerforces during the press-fit and to prevent the piezoelectric frombreaking is to put additional metal layers on the mechanical contactsides of the piezoelectric. But this time and labor to do so increasescosts.

FIGS. 67–69 show a piezoelectric element 22 with a specially shaped end170 that is configured for press-fitting into recess 28. The end 170 caneliminate the need for additional metal layers and result not only incost savings, but also in fewer mechanical contact surfaces andtherefore in better performance. The new piezoelectric shape can alsogenerate a more defined contact area.

The shaped end 170 has at least on one flat 172 adjoining an edge of thepiezoelectric, and preferably two flats 172 on opposing edges of theshaped end 170. The interior end of the flat 172 joins an incline ortaper 174 that helps widen the hole 28 that the piezoelectric element 22gets pressed into. The taper 174 joins a flat, central contact area 176.

The shaped end 170 is advantageously placed on two opposing ends of thepiezoelectric element 22, the ends that will abut the walls defining theopening 28 and cause the preload on the piezoelectric element. The flats172 on opposing ends 170 are spaced a distance apart selected to allowthe piezoelectric element 22 to be inserted into an undeformed opening28. That helps position the piezoelectric. The inclines 174 make iteasier to press the piezoelectric into the opening 28. The inclinedsurface 174 is of sufficient length and inclination to allow insertionwithout unacceptably damaging the piezoelectric element 22. The specificlength and inclination angle will vary with the particular application.The central contact area 176 defines the final dimension of the opening28 and sets the preload, it also provides a localized contact area toreduce the area in driving engagement with the resonator 24 in which theopening 28 is formed. That helps locate the contact area and axis ofengagement and excitation, and it helps improves the engagement.Advantageously, the shape of the end 170 is symmetric about central axis25 so the piezoelectric can be press-fit from two directions, but thatneed not be so.

The piezoelectric element 22 could be ground after the sintering processthat produces the piezoelectric elements, in order to shape the taper(s)174 and flat(s) 172. Alternatively, the taper could be produced duringthe pressing process by which the piezoelectric elements are formed. Thepressing process typically occurs after the layer stacking process inthe piezoelectric production sequence. In this way no additional processstep is necessary. This method also has an advantage over grinding inthat no electrode surfaces are in danger of being ground, resulting inlower piezoelectric efficiency.

Referring to FIG. 69, the following process is believed suitable toproduce this piezoelectric element, although someone skilled in the artcan devise other methods given the present disclosure. Thelayer-stacking machine starts with the bottom die and places the firstpiezoelectric layer on top. All other layers follow just as in thenormal lay-up process. Finally the top die is placed onto the stack andthe whole stack is then pressed. During the pressing process, thepiezoelectric elements 22 are forced to accept the shape of the die.

The die 178 has a shape configured to produce the depicted surfacecontour. The die 178 thus has flats 172, inclined surfaces 174, andcentral flats 176 located so as to form those surfaces on the pressedand sintered piezoelectric elements produced by the die. The contours ofthe die 178 are modified as needed to account for shrinkage anddeformation that might occur during formation of the piezoelectricelements.

The combined surface contour is repeated for as many piezoelectricelements 22 as are placed in the die. It is important that the relativeposition of the electrodes 180 matches the position of the die. Thestacking machine can ensure proper alignment. The stacked elements arepressed and produce the group of piezoelectric elements depicted inFIGS. 67–69.

Following the pressing process, the piezoelectric elements will be cutand processed as usual. During the cutting, it may be beneficial toleave the die attached to the stack for stability and alignment. Theresult is a piezoelectric element with said advantages.

If the piezoelectric is shaped as shown in FIGS. 67–68, an additionaladvantage arises. Typically the electrodes 180 are printed onto thesides of the piezoelectric element 22. If machines typically used tomake multilayer capacitors are used, the electrodes 180 partially coverthe edges of the adjacent sides, and here that includes a portion of theelectrode over the recessed flat surface 172. Because this surface 172is sized to fit in the opening 28 without deformation the slightthickness of the added electrode layer does not affect installation. Butif that electrode layer 180 were on a normal, square-ended wall of thepiezoelectric element being press-fit against the walls defining opening28, then the edges of the piezoelectric would be larger than the centerwhich lacks the electrode layer, and that would render a press-fit moredifficult. The piezoelectric shape of FIGS. 67–68 thus eliminates theneed for removing the excess electrode material.

It is also possible to shape the die producing the piezoelectricelements such that the deformation that is caused by the polarization ofthe piezoelectric is accounted for. When polarized, the flat contactarea 176 bulges slightly outward, convex to the piezoelectric element22. To offset this polarizing bulge, the die 178 is advantageouslyformed with a slightly convex surface at the contact surface 176 so thatthe resulting piezoelectric element 22 has a slightly concave surface init at the contact surface 176. The amount of curvature is selected sothat after the piezoelectric element 22 is polarized, the contactsurface 176 is flat. The amount of curvature will vary with the specificdesign of the piezoelectric element involved.

FIG. 75 shows a potential press-fit insertion sequence. Optionally, byfirst inserting a tapered plug 182 into the opening 28, the insertionedges of the opening 28 are preferably slightly plastically deformed,which widens portions of the mating edge of the opening. For theillustrated embodiment the end walls 31 engage the piezoelectric element22 and place it in compression. To avoid overstretching and breaking thesidewalls 29 during formation of the taper, the insertion edges on theend walls 31 can be shaped individually in two separate steps, or theentire frame can be constrained against axial deformation.

When the plug 182 is removed, the piezoelectric element 22 with shapedends 170 is aligned with the opening 28. The flats 172 preferably areable to enter the opening 28, with or without the widened edge producedby plug 182. The inclined edge formed on the end walls 31 definingopening 28 mate with the inclined surface 174 on the piezoelectricelement 22 to provide a sliding insertion to position the piezoelectricelement in the opening 28. The tapered end walls benefit, but are notnecessary for the press-fit to occur. They do, however, have the addedbenefit of inducing asymmetry in the resonator if so desired. If thesidewalls 29 were to engage the piezoelectric element 22 and apply acompressive force, then an inclined surface could be formed on thesidewalls 29 or on the corresponding edges of the piezoelectric element22.

The above discussion described the piezoelectric element 22 ascomprising a plurality of piezoelectric layers. This need not be thecase as a single piezoelectric crystal or ceramic block could be formedhaving the specially configured ends 170.

FIG. 76 shows another advantageous method to press-fit the piezoelectricelement 22 into the opening 28 of resonator 24. To put this inperspective, a short discussion is given of the objectives, the problem,and then the solution.

Repeatability in the performance of the vibratory motors 26 requires aconsistent preload be applied to the piezoelectric elements 22. In orderto accommodate variations in the dimension of the piezoelectric element22, while achieving the same preload, the sidewalls 29 can be placed inplastic deformation. The slope of the stress-strain-curve is very smallin the plastic region, which leads to very small changes in preload whenthe length of the piezoelectric element 22 changes. This allowscombinations of shortest piezoelectric element 22 with the largestopening 28, and the longest piezoelectric element 22 with the smallestopening 28, to result in essentially the same preload on thepiezoelectric element.

But when the piezoelectric element 22 is press-fit into the opening 28,it is subjected to frictional forces that lead to high shear forces onthe piezoelectric element. Because the piezoelectric material isbrittle, the shear forces can act to delaminate adjacent layers of thepiezoelectric material. To prevent shear forces from acting on thepiezoelectric the protective plates 34, 84 can be added to take theshear forces. This not only alleviates the stress on the piezoelectricelement 22, but also helps the press-fit as the plates 34, 84 act toguide the piezoelectric into the opening 28.

To reduce the cost of the vibratory motor 26 and to also improvemechanical coupling between the piezoelectric element 22 and theresonator 24, it is desirable to press-fit the piezoelectric element 22without any protective layers of steel such as plates 34, 84. Thefollowing process allows this by reducing the forces acting on thepiezoelectric during the press-fit operation to a constant and low leveland by making the press-fit process more controllable and thereforeeasier to automate.

The objective is to have most of the elongation of the sidewalls 29 donenot by the piezoelectric being forced into the opening 28, but to havethe elongation done by another machine. This machine pulls the resonator24 with force P as shown in FIG. 76 to stretch the sidewalls 29. Thepiezoelectric with tapered edges 82 sits on top of the opening 28 in theresonator 24 and is pressed into the opening 28 with a force, F, that ispreferably constant, and that is not strong enough to push the piezointo the hole by itself. The force F is also not strong enough to causedamage to the piezoelectric element 22, and is especially not strongenough to cause shear forces that delaminate the piezoelectric material.

At some point during the elongation of the sidewalls 29 by increasingforce, P, the piezoelectric 22 starts to slide into the hole underforce, F. By setting the force, F, to a specified value, shear forcesbetween the piezoelectric element 22 and the resonator 24 are limited tothe resulting normal force multiplied by the coefficient of friction.This resulting normal force equals the desired preload force minus theforce, P.

Once the piezoelectric element 22 starts sliding into the opening 28, itis necessary to stop the elongation of the sidewalls 29 by the machinebecause otherwise the resultant preload on the piezoelectric will bereduced.

The pulling machine applying the force P can be controlled by one of twoprinciples, load control or displacement control. Load control refers tocontrolling the applied load and measuring the resultant displacement.Displacement control is just the opposite: controlling the displacementand measuring the resultant load. To prevent overstretching thesidewalls 29, it is preferable to use displacement control for thisapplication.

The sidewalls 29 could be curved toward, or away from the longitudinalaxis 25 extending through opening 28. If the sidewalls 29 are curvedaway from the longitudinal axis 25 extending through the opening 28,then by applying opposing forces to opposing sidewalls 29, the end walls31 can be forced apart, allowing the piezoelectric element 22 to beinserted into the opening 28. Upon removal of the force pressing thecurved sidewalls 29 toward each other, the piezoelectric element 22 isplaced in compression. Advantageously, in pressing the curved sidewalls29 together in order to enlarge the space between end walls 31, thesidewalls 29 are stressed beyond their elastic limit so as to achievethe advantages discussed herein.

Similarly, if the sidewalls 29 are curved toward each other, then byapplying a force to the sidewalls that urges them apart, the end walls31 are moved away from each other, allowing the piezoelectric element 22to be inserted into the opening 28. Upon removal of the force pressingthe curved sidewalls 29 away from each other, the piezoelectric element22 is placed in compression. Advantageously, in pressing the curvedsidewalls 29 apart in order to enlarge the space between end walls 31,the sidewalls 29 are stressed beyond their elastic limit so as toachieve the advantages discussed herein.

Instead of tapering the piezoelectric element 22 by applying inclinedsurfaces 82 (or 174 (FIGS. 67–69) it is also possible to taper the edgesof the opening 28. It is also possible to have both parts tapered. Ifneither the piezoelectric element 22 nor the opening 28 are tapered, thepiezoelectric element 22 starts to slide in at the point where thepiezoelectric element and the opening are the same size. This presentsalignment problems and requires very precise control to avoidoverstretching of the sidewalls 29. Therefore, it is desirable to haveat least one mating part tapered.

The press-fit method described here is also adaptable to all otherpress-fits. The vibratory motor 26 with the piezoelectric element 22 andthe resonator 24 or frame, is used as an example.

Stepper Motor Approximations

Referring to FIG. 70, the vibratory element 26 can be operated at aselected excitation frequency that does not coincide with any frequencybeing used for regular operation of the motor assembly 22 and thattherefore does not transport the driven element 42 in a specifieddirection, but rather excites a mode of vibration in the driven element42 itself. This is illustrated in FIG. 70, where the induced mode of arod-shaped driven element 42 has nodes 190. Similar nodes are observedif the driven element is a rotational object such as in FIG. 4.

In this situation, there is a tendency for the rod 42 to shift itsposition so that the contacting portion 44 becomes centered at the node190. Depending on what node is closest to the contacting portion 44,this results in a forward or backward motion of the rod 42. Thus, byseeking out a specific position along the driven element 42, the motorassembly 22 can provide the incremental movement and locating aspects ofa stepper motor. The step sizes are determined naturally by theparticular mode of vibration that is being excited in the driven element42, and will vary with the mode that is being excited.

Centering the driven element 42 at known nodes 190 can be exploited tomove the driven element 42 into a pre-defined position. This eliminatespositioning errors that may have accumulated during regular operation ofthe vibration motor 26 and can be used to increase the accuracy andrepeatability of the motor without the need of position feedback. Thismode of operation requires that the actual position of the drivenelement 42 be within a certain distance to a desired node 190, so thatthe resonant vibration causes movement toward the desired node.

The suspension of the driven element 42 affects the frequencies and nodelocations of the natural vibration modes of the driven element 42. Forthe purpose of stepping the driven element 42, the influence of thesuspension must therefore be considered in choosing appropriateexcitation frequencies to achieve this locating activity achieved by thenodes 190. Conversely, the design of the suspension may be influenced bythe need for particular excitation frequency or frequencies and designedto achieve those frequencies. There is thus provided a method andapparatus for using the vibration nodes of the driven object totransport the driven object to a known position for calibration.

Position Sensing

There are situations where it is desirable to exactly know the positionof the driven element 42 relative to the vibration element 26. Referringto FIG. 71, an illustrative implementation is described that uses thecharacteristic travel duration of a vibration or acoustic pulse from thepiezoelectric element 22 to monitor the position of the driven element.The position of the driven element 42 relative to the vibration element26 can be determined by measuring the time it takes for a mechanicalvibratory pulse to travel from the vibration element 26 into and throughthe driven element 42, and/or vice versa. The vibratory pulse can begenerated in the vibration element 26 by the piezoelectric element 22 orin the driven element 42 by some other generating mechanisms 198, suchas a solenoid, a spring driven impact mechanism, or other mechanical orelectronic mechanisms.

A receiver 196, e.g., a piezoceramic microphone, that is mountedadjacent a distal end of the driven element 42 at a known location onthe driven element can be used to sense the pulse generated by thepiezoelectric element 22, the pulse being sufficient to cause an impactvibration at the selected contacting portion 44. Alternatively, thepiezoelectric element 22 can be used to sense the vibratory pulsegenerated by the generator 198 by exploiting the piezoelectricmaterial's inherent ability to convert a mechanical movement (e.g., ofselected contacting portion 44) back into an electrical signal.

It is also possible for the piezoelectric element 22 to sense avibratory pulse that it has generated earlier. This requires that thepulse travel through the vibratory element 26 and the driven element 42,be reflected at a location on driven element 42, such as the distal endof the driven element 42, and return to the piezoelectric element 22where it can be sensed. In a similar fashion, by way of reflection, itis possible for a sensor 196 to sense a pulse generated by a generator198.

The vibratory pulse can be chosen such that its power spectrum does notcontain significant vibratory energy at frequencies that could cause thedriven element 42 to move. Alternatively, the vibratory pulse can beincorporated into the operational input signal to the piezoelectricelement 22, for example in form of a brief pause. Because the geometriesand material properties of the vibratory element 26 and of the drivenelement 42 are known, and because the position of the contacting portion44 on the vibratory element 26 is known, the monitored time differencebetween pulse generation and sensing is representative of orcharacteristic of the distance between the piezoelectric element 22 andthe receiver 196 or a distal end of the driven element 42.

In some of the various position-sensing embodiments, it is desirablethat the piezoelectric element 22 is temporarily deactivated prior tothe position sensing so that undesirable vibrations are allowed todampen out. Then the specified signals can be emitted and detected, withthe operation of the vibrator element 26 resuming thereafter. It is anadvantage of some of these embodiments that, if the piezoelectricelement 22 is used as a sensor as well as actuator, only a singlepiezoelectric element is needed to move the driven element 42 as well asprovide position feedback.

The pulse generated in either the piezoelectric element 22 or in agenerator 198 is reflected at any surface where the mechanical impedancechanges abruptly. These surfaces include the opposing ends of thevibrating element 26 and the opposing ends 200 of the driven element 42.Some of these reflections are undesirable and must either be masked orbe otherwise distinguishable from the position-determining pulse. Waysto achieve this include, but are not restricted to, degrading undesiredreflected signals by inclining, damping or roughening certain reflectingsurfaces such as the distal end 200 b of the driven element 42. Giventhe present disclosure, other ways of altering the ends 200 could bedevised to allow signals reflected from the ends to be distinguished foruse in the position sensing method and system.

FIG. 72 shows a different position-sensing embodiment that uses aresistive position measurement method that uses characteristicresistance of a resistive driven object to monitor the position of thedriven object in a way that is analogous to how an integratedpotentiometer operates. The position of the selected contact portionalong the length of driven element 42 varies a resistance that isdetected and used to define a relative position of the elements.

For illustration, the driven element 42 comprises a cylindrical rod. Thedriven element 42 is either made of an electrically resistive material,or it is made of an electrically insulating material that has beenentirely or partially coated with an electrically resistive material204. A carbonated plastic material is believed suitable for either use.Since the electrical resistance between the selected contacting portion44 of vibratory element 26 and either of the opposing ends of the rod 42depends on the position of the contacting portion 44 relative to the rod42, the position can be determined by measuring the electricalconductivity, or the electrical resistance, between one of the opposingends of the rod 42 and the vibration element 26.

The voltage that is necessary for measuring the electric resistance canbe small and it can be applied between the vibrating element 26 and adistal end of the driven element 42. Preferably though, one end of thedriven object 42 is connected to a positive supply voltage and the otherend to a negative supply voltage. By measuring the voltage at thevibration element 26, e.g., by a voltmeter 204, accurate positioninformation can be obtained.

Instead of applying the necessary voltage directly to ends 200 a, 200 bof the driven object 42, this voltage can also be applied to the wheelsor bearings 46 supporting the driven element 42 provided that the wheelsor bearings 46 are made from an electrically conductive material andthat they are electrically insulated from each other and from thevibrating element 26. In such an embodiment, the electrical contactresistance between the bearings 46 and the driven element 26 may have tobe accounted for.

A suitably coated electrically nonconductive driven object 42 for use inthe described embodiment can be cut from a sufficiently thick sheet ofplastic that has previously been dipped into conductive paint and letdry. This forms a conductive layer on the exterior surface of the plate.The plate is then cut into strips creating two opposing edges that haveno conductive layer. Thus, except for the strips or rods formed from thesheet edges, the cutting process advantageously exposes thenonconductive plastic on two elongated sides of the driven object (thestrips or rods), which results in the conductive paint forming anelongated resistor 202 that wraps around the longitudinal axis of thedriven object. This embodiment can be modified by further removing theconductive layer from one of the ends 200 a, 200 b of the drivenelement. The position can be determined from a measurement of theresistance between the vibration element 26 and one contact point, e.g.,bearing 46 a or 46 b.

Electrically conductive driven objects 42 can also be used in positionsensing embodiments if appropriate portions of them are first coatedwith an insulating layer and then with an electrically resistive layer.For example, an insulating layer may be applied to that side of ametallic rod-like driven object 42 that faces the bearings. On top ofthis layer, an electrically resistive layer 202 is applied so that itcontacts the underlying metal only at the ends of rod 42. The positiondependent resistance lies now between a bearing and the end of the rod42.

OTHER VARIATIONS & ADVANTAGES

In comparison to prior art piezoelectric motors, the present motor 26requires only one piezoelectric element 22 and only one electricalexcitation to generate motion. Due to the use of resonant vibrationmodes to generate elliptical motion 100 with a single excitationfrequency, the piezoelectric element 22 can be smaller than those ofother bi-directional piezoelectric motors can, and the overall motor 26can also be smaller.

The present invention works very well to provide linear motion of drivenelements 42. The traditional solution is to use a motor with a gearboxdriving a rack and pinion arrangement. The present motor assembly 20provides a simpler arrangement, and less costly arrangement than priorart motors. Because the selected contacting portion 44 engages thedriven element 42 by friction, the motor 20 is not damaged if the drivenelement is externally pushed so as to back-drive the motor. In contrast,such motion would strip the gears of conventional electric motors.

The present invention is especially suited for low cost applications.The simple design can avoid the need for precision manufacturingrequirements and the attendant cost. It allows low cost manufacturingmethods and inexpensive piezoelectric elements. In return, the designprovides less power and efficiency than some other piezoelectric motors.But the available power and low cost make the embodiments of thisinvention especially suitable for many traditional markets, such astoys, office equipment, and home automation. Some illustrative examplesof the uses for the vibratory motor 26 are given below. But onesignificant advantage of this motor is its size and simplicity, whichcan result in low cost.

Vibratory motor assemblies 20 are believed possible that are as small as0.4×0.4×0.8 inches (1×1×2 cm) in size, moving driven elements 42 at0.5–10 inches per second (1.3–25 cm/sec), with a force of 0.1–3 N.Rotational drive units are believed possible with sizes as small as0.6×0.8×0.8 inches (1.5×2×2 cm) with torques and revolutions per minute(RPMs) depending on the diameter of the rotationally driven object 42.The voltage of the vibratory motor assemblies can be varied depending onthe circuit design and the power needed, but can range from 3V, 6V, 12V,24V 48V, 110V or 220V. Other custom voltages can be used. There is thusa wide range of operating voltages available for the vibratory motors26.

The size of the vibratory element 26 can be very small, with elements assmall as 2×3×10 mm³ believed possible. The cost of the vibratory motors20 is believed to be half that of competing electric motors. Thesemotors 26 can produce linear motion, rotary motion, both linear androtational motion, and blocking force when un-powered. They start andstop without delay in as little as 0.6 milliseconds, have no backlashbecause there are no gears, and can provide fast motion yet also provideslow motion without using gears. They are inaudible because they aredriven in the ultrasonic range. The motors require no lubricants and useno toxic substances. They are very accurate and can move in themicrometer range if needed. By controlling the times during which theyare powered, they can achieve various speeds and distances. Theygenerate no magnetic fields, have no brush discharge, and no inductivevoltage peaks.

The advantages of the vibratory motors 26 make them very suitable foruse in CD-ROMs as tray actuators, in scanners to move the light bar orrotary elements, in printers and copiers to transport and guide paper.In home automation applications, the vibratory motors 26 could actuateair conditioning elements, automatic blinds, lighting controls andswitches, dust protection doors on dust sensitive appliances, automaticlocks, , or elements in motion detectors. The vibratory motors 26 couldalso be used to position, pan, tilt or zoom remotely operated cameras,e.g., security cameras.

The ability to directly engage and drive glass offers advantages forusing the vibratory motor 26 to control the position and focus of accentlighting in homes, retail stores, theaters, galleries, museums, hotelsand restaurants. In automotive applications, the vibratory motors 26 canbe used to position mirrors, headlights and air conditioning vents, andto actuate automatic locks. The stepper-like operation of the motorassembly 20 allows the storing and retrieving of mechanical settings,such as mirror position, for each of several drivers under the directionof a computer.

The combination of a computer that stores position information inconnection with a positionable motor 20 finds many possibilities insensors that automatically adjust their position. These include opticalsensors, lens cleaning mechanisms for such sensors, protective coversthat open and close by the use of vibratory motors 26, automaticalignment mechanisms, proximity lasers, and adjustments of a variety ofproducts that require movement of small parts by simple motors.

The vibratory motor 26 is especially useful for toys due toadvantageously low cost, small size and low noise. Dolls could havelimbs moved and eye lids actuated by the motors 26. Remotely controlledvehicles could have steering controlled by the motors 26. Animated toybooks could be provided. Railway models could have moving forks, cranes,signals, railway gates and other actuated components. Various otherapplications of the motor 26 can be made. Further, the vibratory motor26 can be made resistant to liquids, such as water, with appropriatemodifications and coatings, and can provide multiple motions. The lowforce output reduces the possibility of injury. Also, it is possible tomix the electrical operating signal that is supplied to thepiezoelectric element 22 with an electrical signal that contains anon-operational yet audible frequency spectrum. In such an embodiment, apiezoelectric motor 20 can also serve as a simple device for generatingsound and music.

There is thus advantageously provided a motor assembly 20 that costsless to produce than traditional motors of comparable power and speed.The size and weight of the motor assembly 20 is less, and the inventionallows for exceptional miniaturization of the motor. The motor canachieve stepper-like motion of the driven elements 42, and positioningof the driven elements is possible without using positioning sensors onthe driven part. The motor assembly 20 allows the use of fast, or slowdriving speeds, and does not need a gearbox. Because the motor does notuse gears, there is no backlash as associated with gear trains. Themotor assembly 20 allows the driven element 42 to be translated, orrotated, or both. The positioning of the driven element 42 haspositioning accuracy of 1 μm. The operating frequency can be selected tobe inaudible to humans so that motor operation is silent. Due to theabsence of magnetic fields or spark discharges, the motor assembly 20and its vibratory element 26 are suitable for use in environments thatare sensitive to electromagnetic interference or sparks. Quick reactiontimes of the motor assembly 20 permit control with binary statecontrollers, which are easier to implement and less expensive than PIDcontrollers.

The invention further advantageously provides a vibratory element 26having a piezoelectric driving element 22 and a resonator 24 thatadvantageously holds the driving element 22 in compression. Thisvibratory element combined with a resilient suspension system such asspring 10 can advantageously be provided to users who apply thecomponents to a variety of driven elements at the discretion of theuser. These parts are advantageously designed and configured tocooperate to generate an elliptical path 100 at a selected drivingportion 44 for one or more predetermined applications or for one or moregeneric applications. This combination can be provided as a unit, andcould be provided with or without the spring 50. A user could thus usethese components to drive a variety of driven elements 42.

Alternatively, a user could be provided with a complete motor assembly20 containing not only the vibratory element 26 and resilient mount suchas spring 50, but also driven elements 42 supported in a predeterminedrelation to the vibratory element 26. In this alternative situation, themotor assembly 20 is preferably encased in a housing along with asuspended driven object 42, as for example a rod for a linear motor. Inthis alternative situation, the motor assembly 20 and driven element 42are ready for installation and use as the user sees fit. The assemblycan be used with a driven element used in other motors, or it could beused as a part of a product configured for use with the components.Providing the driving elements and suspension elements allows the userto acquire a low cost driving mechanism having great flexibility in itsapplication.

The driven object 42 preferably has a smooth and hard surface located toengage the selected driving portion 44. The driven element 42 can have avariety of shapes, for example it can be a disc, a rod, a wheel, a gear,a beam, a ball, etc, as long as a fairly constant contact force can bemaintained between the selected contact portion 44 and the drivenelement 42. This gives designers a wide range of possible implementationmethods for the motor assembly 20.

The motor assembly 20 is advantageously encased in a housing to protectit from dirt and other extraneous contact and potential damage. Thehousing can be manufactured out of plastic through an injection moldingprocess, or made of sheet metal. It is preferably designed such that itcan be assembled through snap joints. This assembly avoids the use ofmore expensive methods including threaded fasteners and is good for afully automated assembly.

This provides the possibility for the end user to have an inexpensiveand small motor unit, which is easy to implement into a design. In orderto increase the flexibility of use, the base 10 or the housing can haveclamping holes or other clamping mechanisms to make it easier to attachto the end user's product. If the volume of a specific designed base 52or housing is sufficient, the base 52 and/or housing unit could bespecially configured to meet the mounting needs of the user.

There is thus provided a mechanism and method for generating an ellipse100 that has a first semi-axis and a second semi-axis, with the lengthof the first semi-axis being useful to generate a difference in frictionforce between the selected contact portion 44 and an engaging surface ofa driven element 42, during the motion components in the direction ordirections of travel along the elliptical path 100. This ellipticalmotion is advantageously provided by a single excitation frequencyprovided to a piezoelectric element 22 that results in at least twovibrational modes generating the elliptical path 100. This ellipticalmotion 100 is achieved by exciting at least two vibrational modes atleast one of which, and preferably both of which, are not purelongitudinal or pure bending modes, and superimposing those modes togenerate the elliptical motion at the selected contacting portion. Thiselliptical motion 100 is advantageously achieved without having to placethe selected contacting portion 44 into contact with any driven element42.

The practical result of having modes other than purely longitudinal andpurely bending, is that the major axis defining the elliptical path 100of the selected contacting portion 44 is angled relative to thelongitudinal axis 25 of the vibratory element 26. The major and minoraxes of the elliptical path 100 are not aligned with the longitudinalaxis 25 of the resonator as is common with prior art vibratory devices.The angle of the major axis of the elliptical path 100 relative tolongitudinal axis 25 is advantageously not near 0 degrees or multiplesof 90 degrees. For ease of description, the angle will be describedrelative to the orientation of parts in FIG. 1 in the first quadrant,but one skilled in the art will appreciate that the parts can be rotatedthrough other quadrants or that the orientation of parts can bechanged—without altering the relative angles discussed here.

Because the greatest motion and fastest rate of travel is achieved whenthe longitudinal axis of the elliptical path 100 is aligned with thetravel path of the driven element 42, the vibratory element 26 ispreferably angled relative to the driven element 42 in order to alignthose axes. If the major axis of the elliptical path 100 aligns with thelongitudinal axis of the driven element 42, then this above-discussedangle can be considered to be the angle α, discussed above. The perfectalignment of the major axis of the elliptical path 100 with thelongitudinal axis of the driven element 42 is often compromised forpractical reasons.

Because the elliptical motion 100 is angled relative to the longitudinalaxis 25 of the resonator 24, elliptical motions with large aspect ratioscan be used. Ratios of the major to minor axes of the elliptical path100 are advantageously over 5, more advantageously over 10, andpreferably over 20 to 1. But when the semi-axis becomes too small, theselected contacting portion may not adequately disengage from the drivenelement when the ellipse is aligned with the driven element and thusratios of 30:1 or more are difficult to achieve, especially at low cost.Further, as the ratios increase, the performance approaches that of animpact drive vibrator element. Thus, ratios of over 150:1, and even 30:1are difficult to achieve and use. While most useful sized ellipticalpaths 100 are believed to have aspect ratios of about 3:1 to 150:1,preferably the ratios are from about 4:1 to 30:1, and ideally from about5:1 to 15:1. If aspect ratios are used up to and over 150:1, then theresulting applications find use primarily in impact drive types ofdevices.

The amplitudes needed to achieve elliptical path 100 at the selectedcontacting portion 44 are preferably obtained by large magnification ofsmall input signals. That requires selecting or creating resonance modesof vibration sufficiently close to the selected input signal to achievea usable amplitude. Advantageously, for each volt input to thepiezoelectric element 22, the selected contacting portion 44 can achieve0.3–0.5 microns of motion along the major axis of the elliptical path100. Preferably, for each volt input, the motion along the major axis ofthe elliptical path 100 is 1 micrometer or greater. These motions arethe result of resonant vibration mode amplifications that increase themotion by factors of at least 100, and typically by factors of 1000 ormore.

It is possible, but less desirable, to use a small resonancemagnification and instead provide a larger input signal in order toachieve the needed amplitude to generate an acceptable elliptical path100 at the selected contacting portion 44. If one of the vibration modesthat results in the usable elliptical path 100 is off-resonance, thenthe electric input signal to the piezoelectric element 22 can beincreased sufficiently to result in a usable elliptical motion, onesufficient to moves the driven element 42. Thus, it is believed suitablein some applications to have one volt input to the piezoelectric element22 result in motion along the major axis of the elliptical path of 20–50nanometers, but with movements of 100 nanometers or more beingdesirable.

Thus, the selected contacting portion 44 moves in a first ellipticalpath having a major axis and minor axis when the vibration source, suchas piezoelectric element 22 is excited by a first electrical signal thatcauses at least two vibration modes that are superimposed to create thefirst elliptical path 100. Preferably, at least one of the vibrationmodes is other than a pure longitudinal mode and other than a purebending mode. When at least one of the two vibration modes isoff-resonance, the first electrical signal is amplified sufficiently tocause the at least one off-resonance vibration mode to produce a motionof the selected contacting portion 44 having sufficient amplitude thatthe resulting elliptical path 100 can move the driven element 42 duringuse. As used here, the reference to an off-resonance vibration moderefers to a vibration mode that is sufficiently away from the resonancemode that the resulting motion does not generate a usable ellipticalmotion, motion insufficient to drive the driven element 42.

The desired elliptical motion 100 is advantageously achieved withoutrequiring the selected contacting portion 44 to engage the drivenelement 42. Depending on the angle of engagement, reflected by angle α,the engagement can cause impact or bending that may affect theelliptical path 100 or the resulting motion of the driven element 42,and appropriate compensation can be made for those effects.

As mentioned above, the generation of the elliptical path 100 at theselected contacting portion is most easily determined in a localizedcoordinate system that does not align with the longitudinal axis 25 ofthe vibratory element 26. A coordinate transformation to align themotion so that one axis of the elliptical path 100 aligns with thevibratory element 26 or preferably with the driven element 42 allows thepractical use of the elliptical path 100 to be evaluated.

If multiple motions of a driven element 42 are desired to be producedfrom a single vibratory element 26, then the selected elliptical path100 is likely to be a compromise among several potential ellipticalpaths at various frequencies, and if desired, at several selectedcontacting portions 44. If multiple motions are desired to be producedby a single piezoelectric element 22, it is preferable that thefrequency used to achieve the different elliptical motions besufficiently different to clearly separate the frequencies and theirresulting motions. The frequencies for the separate motions arepreferably separated by at least the same margin as the frequency rangeover which the substantially uniform elliptical motion 100 is achieved.Thus, for example, if a first elliptical motion 100 is achieved over afrequency range of 2.5 kHz on either side of a first frequency, for atotal range of 5 kHz, then the second frequency is advantageously atleast 5 kHz from the first frequency, and preferably more.

Ideally, the major axis of the elliptical path 100 is aligned with theaxis along which the driven part 42 moves. As shown in FIG. 1, thatalignment angle corresponds to the angle α between the longitudinal axis25 of the vibratory element 26 and the axis 45 of a rod-like drivenelement 42. This alignment may be achievable if the driven element 42 ismoved in only one direction. But when the same vibratory element 26 isused to move the driven element 42 in opposing directions, relativealignment is difficult or impossible to achieve, especially in bothdirections. Further, the alignment considerations for bi-directionalmotion as discussed below is advantageously used even when only a singledirection of motion of the driven element 42 is used.

FIG. 81 will be used to illustrate the considerations in this alignment.FIG. 81 illustrates a first elliptical path 100 a having a major axise_(x1), for moving the driven element 42 in a first direction, and asecond elliptical path 100 b having a major axis e_(x2) for moving thedriven element in a second, opposing direction. The major axis e_(x1),is inclined at an angle β₁ relative to axis 45 of the driven element 42and the major axis e_(x2) is inclined at an angle β₂ relative to thataxis 45. The axis 45 can be viewed as parallel to a tangent to thedriven element 42 in the direction of motion of the driven element 42 atthe selected contacting portion 44. The motion along the firstdirection, the motion resulting from ellipse 100 a is believed totypically be the easiest to achieve and will typically have the majoraxis e_(x1) of ellipse 100 a most closely aligned with the axis 45 ofthe driven element 42, while the major axis e_(x2) is not as closelyaligned with that axis 45. Thus, β₁ is typically smaller than β₂ when β₁is selected first. But that need not always be the case as the ultimateselection of elliptical paths 100 a, 100 b is a result of compromisingseveral factors as discussed herein.

While it is ideal for β₁ and β₂ to be 0, so that the major or minor axesof the elliptical paths 100 to align as closely as possible with thedesired motion of the driven element 42, that is difficult to achievefor multi-direction motion. For bi-directional motion where the samemotion is desired but in different directions, it is believed that β₁and β₂ will range from 5 to 40 degrees with respect to a tangent to thedriven element 42, along the direction of motion of the driven element42, at the selected contacting portion 44. It is believed possible, butless desirable to have the angles go from 40 to 45 degrees. It is verydesirable to have the angles β₁ and β₂ perfectly align the major axis ofthe elliptical paths 100 a, 100 b with the direction of motion of thedriven element, and preferably align them within 0 to 5 degrees. As usedherein, because the orientation of parts can increment the anglesthrough various multiples of 90 degrees relative to a horizontal axis,the angles given should be construed as relative angles rather than asabsolute numbers. Thus, for example, the reference to aligning the majoraxes and the driven path within 0 to 5 degrees includes angles onopposing sides of the horizontal X-axis as shown in the drawings. Thatthus includes an absolute angle of 360–365 degrees relative to a commonaxis of measurement.

As shown in FIG. 81 the angle is relative to the axis 45 of thetranslating rod 42. But the driven element 42 could comprise a rotatingdisk (e.g., FIG. 4). Usable but sometimes undesirable performance isbelieved to be achieved if β₁ and β₂ range from about 5 to 85 degreesfrom the tangent to the driven element at the location of the selectedcontacting portion 44. Preferred performance levels are believed to beachieved if β₁ and β₂ range from about 5–35 degrees and 55–85 degrees,and the best performance is believed to be achieved when β₁ and β₂ rangefrom about 15 to 25 degrees and 65 degrees to 75 degrees.

As stated or implied above, because of symmetry considerations relativeto the 0 and 90 degree axes, the above range can vary in 90 degreeincrements in absolute value relative to a common axis of origin. Theabove discussions and angle ranges are believed to apply tomulti-direction motion.

In order to achieve the desired angles β₁ and β₂, it is believed thatthe angle α should be maintained within the previously discussed ranges.The particular combination of β₁ and β₂ that is used is typically chosenso that the major axis of elliptical paths 100 aligns as close aspossible with the axis of the driven element 42. The closer thealignment, the more efficient the transfer of motion from the vibratoryelement 26 to the driven element 42 along the selected axis of motion45.

But from the various angles discussed, it can be observed that theselected vibration mode(s) of the resonator 24 that result in usablevibratory motions along elliptical paths 100 orientated at angles β₁ andβ₂, are neither purely longitudinal nor purely bending modes. Thus, inproducing the elliptical motion 100 at the selected contacting portion44, the angles β₁ and/or β₂ are such that the major and minor axes ofthe elliptical paths 100 a, 100 b do not align with the longitudinalaxis of resonator 24 of the vibratory element 26. Further, the angles β₁and/or β₂ are such that the major and minor axes of the elliptical paths100 a, 100 b do not align with a pure bending mode of that vibratoryelement 26, e.g., along axes 38, 40 in FIG. 1. The angle ∝ between thedriving element such as vibrating element 26 and the driven element 42is varied in order to allow the advantageous alignment of the major andminor axes with the direction of motion desired for the driven element42.

This also means that the vibrational modes of the vibratory element 26that generate elliptical paths 100 a, 100 b at the selected contactingportion 44, have at least one vibration mode that is not a purelylongitudinal vibration mode along axis 25, and not a pure bending mode(e.g., along the axes 38, 40 for the configuration depicted in FIG. 1).Thus, for example, the two vibration modes being selected to generateelliptical path 100 a preferably do not include a pure longitudinal orpure bending mode of the resonator 24 in order to produce the firstelliptical motion 100 a of the selected contacting portion 44, and thesame is true with the vibration modes to generate the second ellipticalpath 100 b. If a pure longitudinal or pure bending mode is used togenerate the first elliptical path 100 a, then the vibration modes usedfor the second elliptical path 100 b do not necessarily include a purelongitudinal or pure bending mode of the resonator 24 in order toproduce the elliptical path 100 b. Further, if a vibration mode is usedthat includes a pure longitudinal vibration mode along axis 25, thendesirably the axis 25 is inclined to the driven element 42 at an angle αthat is other than 0 and 90 degrees or multiples thereof, and that ispreferably between about 5–85 degrees and multiples thereof.

As the angles β₁ and β₂ become greater relative to the driven element42, the contact results in greater impact between the selectedcontacting portion 44 and the driven element 42. When the aspect ratioof one or both elliptical paths 100 a, 100 b becomes large, so that oneaxis is much larger than the other axis, the contact approaches that ofan impact drive. It is believed possible to have one of the ellipticalpaths 100 a, 100 b have a high aspect ratio, sufficiently high that theresulting motion can effectively be considered an impact drive, and havethe other elliptical path with a lower aspect ratio to produce anon-impact drive. Advantageously, aspect ratios of the elliptical paths100 that produce a pure impact type drive, are avoided.

Further, it is believed possible that the teachings of this disclosurecan be used to configure a vibratory element 26 having very high aspectratio elliptical motions 100 a, 100 b in opposing directions. When theaspect ratio of the major to minor elliptical axes become great enough,the particular direction of motion around the elliptical path is notdeterminative of the direction in which the driven element moves.Instead, the angle of inclination β of the major axis relative to thedriven element becomes the determinative factor in deciding thedirection of motion. Thus, it is believed possible to use two highaspect ratio elliptical paths 100 a, 100 b, at the same (or different)selected contacting portions 44, to create an impact drive moving thedriven element 42 in the same direction. Indeed, the principles of thisdisclosure could be used to have a single piezoelectric element 24generate two longitudinal resonance modes at two different frequencies,each of which is used in an impact drive.

Whether high aspect elliptical motion is used to approximate pure impactdrive, or whether a pure linear motion is achieved to implement animpact drive, the motion of the driven element 42 can be achieved at twoseparate frequencies. But the use of two frequencies can result indifferent rates of travel of the driven element. The differences in therate of travel by using different frequencies can be enhanced if a highaspect elliptical motion is used in which the direction of travel of theellipse (e.g., clockwise v counter-clockwise) changes, or in which theangle β, changes. Further, the teachings herein can be used even if morethan a single piezoelectric element 22 is used to cause the multiplefrequencies for the impact-type motion or to cause actual impact motionusing mainly longitudinal resonance of the vibratory element 26.

It is desirable to have the angles β₁ and β₂ be reasonably constant overas wide a range of excitation frequencies to vibratory driving element22, as possible. For example, if any excitation frequency signal topiezoelectric element 22 over a 2 kHz range results in elliptical motion100 at the selected contacting portion where the angle β₁ does not varyby more than 5 degrees, then it becomes easier to design the vibratorysystem, and it becomes easier to allow the use of components with largertolerances in performance parameters. It is desirable to have the anglesβ₁ or β₂ vary less than 10 degrees, and preferably less than 5 degrees,and ideally less than 3 degrees, over as large range of excitationfrequencies as possible. This allows the angle α of inclination betweenthe predominant axis 25 of the vibrating element 26 and the motion axis45 of the driven element 42 to be set with reasonable tolerances, and touse components with tolerances obtainable at affordable prices, andproduce acceptable motion. This especially allows the use of low costmotors in a wide variety of commercial applications, as discussedherein.

It is thus desirable to have the selected contacting portion 44 move inapproximately the same elliptical path 100 when the frequency of thedriving signal input to the piezoelectric element 22 varies by as littleas 200 Hz on either side of the selected frequency. Advantageously,approximately the same elliptical path 100 is achieved when thefrequency of the driving signal varies as much as 2.5 kHz, or more, fromthe selected frequency. It is thus desirable that the excitationfrequency to the source of vibration 22 can vary by as much as 2.5 kHzon either side of the selected frequency, and preferably greater, whilestill producing suitable amplitudes for elliptical paths 100 at theinclination angles β₁ and β₂. In relative terms, it is desirable to havea range of 5–10% of the selected excitation frequency achieve suitableelliptical paths 100, with the inclination angles β₁ and β₂ varying lessthan 25 degrees, and preferably less than 10 degrees, and ideally byabout 5 degrees or less, over that frequency range. The ability to do sowill vary with the particular design criteria and performancerequirements.

One way to help maintain the inclination angles , β₁ and β₂ reasonablyconstant over a reasonably wide range of excitation frequencies is tovary the various design parameters of the motor as discussed herein. Theabove discussed angles of 25 degrees, preferably 10 degrees and ideallyabout 5 degrees or less are each considered to be reasonably constant,with angles of about 5 degrees or less being the most preferred and mostreasonably constant. Maintaining these inclination angles reasonablyconstant is most easily achieved by having the effect of the relativephase change on the angles β₁ and β₂ compensate for the effect of theamplitude change on the angle. To achieve this it is useful to select aset of vibration modes that have suitable directions of motion andfrequency response curves for phase and amplitude. Further, using acoordinate transformation to view and analyze the elliptical motion 100in a localized orientation also makes the design easier.

As used herein, the predominant axis is used to indicate an angle ofinclination between the vibratory element 26 and the elliptical path 100of the selected contacting portion 44. The predominant axis will varywith the geometry and shape of the vibratory element 26, and thelocation and orientation of the selected contacting portion 44 on thevibratory element 26. For elongated vibratory elements 26 with theselected contacting portion 44 located at a distal end, as in FIG. 1,the predominant axis is likely to be the longitudinal axis 25, or anaxis orthogonal thereto, or a rotation about such axes. For non-straightvibratory elements 26 as shown in FIG. 77, with the selected contactingportion 44 located on a distal end, the predominant axis is the axis 25through the distal end, or an axis orthogonal thereto, or a rotationabout such axes. For selected contacting portions 44 n located along thelength or on intermediate portions of vibratory elements 26 as shown inFIG. 6, the predominant axis is again the longitudinal axis through thedistal end 36 a, or an axis orthogonal thereto, or a rotation about suchaxes. The particular predominant axis will vary in part with the motionof the selected contacting portion 44 and an adjacent axis of thevibratory element 26 that can be readily used for orientating thevibratory element to achieve alignment of the elliptical path 100 at theselected contacting portion 44 with the driven element 42.

To test the quality of a motor 20 after it has been assembled, it isadvantageous and cost-effective to measure a few electromechanicalcharacteristics of the motor using its piezoelectric element 22. Thecharacteristics include, but are not limited to, the current that isdrawn by the piezoelectric element 22 for a predetermined input signal,and the electrical signal that is generated by the piezoelectric elementwhen it is turned off after having appropriately excited vibrations inthe vibration element 26. It is also possible to track thesecharacteristics during the lifetime of a motor 20, and in doing so tomonitor motor efficiency without the need of special equipment such as alaser vibrometer.

The above disclosure focuses on using a single electrical signal toexcite a single piezoelectric element 22 to produce an elliptical motion100 at the selected contacting portion 44 that is inclined to thepredominant driving axis (e.g., longitudinal axis 25) of the resonator24. That elliptical motion 100 is an unrestrained motion of the selectedcontacting portion 44 and occurs whether or not the contacting portion44 engages the driven element 42. But that inclined elliptical motion100 can be produced by using more than a single piezoelectric element 22on the resonator 24. This invention thus has broader applicability tovibratory elements 26 that use plural piezoelectric elements 22 toachieve the elliptical motion 100 inclined to predominant driving axis(e.g., the longitudinal axis 25) of the resonator 24. Thus, for example,as shown in FIG. 81, first and second piezoelectric elements 22 a, 22 bcould be on different portions or sides of resonator 26 (or contactingdifferently located walls defining one or more openings 28 in theresonator 26 as in FIG. 2), in order to produce an inclined ellipticalmotion 100 a at the selected contacting portion 44. A thirdpiezoelectric element 22 c could be on yet another portion of theresonator in order to produce a different elliptical motion 100 b at theselected contacting portion 44. This use of multiple piezoelectricelements 22 a–22 c requires more complex electronics and thus hasdisadvantages, and it may limit the applicability of some aspects of thepresent disclosure. But it illustrates that some aspects of thisdisclosure have applicability beyond use with the single piezoelectricelement 22 as described herein.

The above description is given by way of example, and not limitation.Given the above disclosure, one skilled in the art could devisevariations that are within the scope and spirit of the invention.Further, the various features of this invention can be used alone, or invarying combinations with each other and are not intended to be limitedto the specific combination described herein. Thus, the invention is notto be limited by the illustrated embodiments but is to be defined by thefollowing claims when read in the broadest reasonable manner to preservethe validity of the claims.

1. A piezoelectric drive for moving a driven element, comprising: apiezoelectric element separate from and drivingly connected to aresonator, the resonator being formed of a single piece of material andhaving opposing ends, the resonator having a contacting portion ininteractive connection with a driven element to move the driven elementduring use of the drive; and a spring connected to the resonator betweenthe ends and spaced apart from the ends a distance, the springresiliently holding the resonator with respect to the driven element,wherein the mass distribution of the resonator between the piezoelectricelement and the contacting portion is different than the massdistribution between the piezoelectric element and the other end of theresonator.
 2. The piezoelectric drive of claim 1, wherein the drivenelement has a cylindrical surface and the resonator has a contactingportion in interactive connection with the cylindrical surface to rotatethe driven element.
 3. The piezoelectric drive of claim 2, wherein thepiezoelectric element comprises a plurality of piezoelectric plates thatare disposed parallel to each other and electrically interconnected tovibrate in the same direction.
 4. The piezoelectric drive of claim 2,wherein the first and second directions are opposite.
 5. Thepiezoelectric drive of claim 2, wherein the spring fastens to thepiezoelectric element.
 6. The piezoelectric drive of claim 1, whereinthe spring fastens to the resonator.
 7. The piezoelectric drive of claim2, wherein the spring fastens to both the resonator and thepiezoelectric element.
 8. The piezoelectric drive of claim 2, whereinthere are two springs each connected to the same piezoelectric element.9. The piezoelectric drive of claim 8, wherein the piezoelectric elementhas a longitudinal axis and at least a portion of the spring is parallelto that longitudinal axis.
 10. The piezoelectric drive of claim 2,wherein at least a portion of the spring is parallel to but offset froma longitudinal axis of the resonator.
 11. The piezoelectric drive ofclaim 2, wherein the spring has an end attached to the resonator and thespring portion abutting that end is not parallel to a longitudinal axisof the resonator.
 12. The piezoelectric drive of claim 10, wherein thespring is L-shaped.
 13. The piezoelectric drive of claim 2, wherein thespring has a first end mounted to a base and an opposing end fastened tothe resonator, with a first leg of the spring parallel to the resonatorand a second leg perpendicular to the first leg.
 14. The piezoelectricdrive of claim 2, wherein the spring is a flat strip of metal.
 15. Thepiezoelectric drive of claim 2, wherein the selected contacting portionis at one end of the resonator and the mass of the resonator between thepiezoelectric element and the contacting portion is greater than themass of the resonator between the piezoelectric element and the otherend of the resonator.
 16. The piezoelectric drive of claim 1, whereinthe selected contacting portion is at one end of the resonator and themass of the resonator between the piezoelectric element and thecontacting portion is less than the mass of the resonator between thepiezoelectric element and the other end of the resonator.
 17. Thepiezoelectric drive of claim 1, wherein the drive has three resonatorsarranged so the contacting portion of each resonator drivingly engagesthe driven element.
 18. The piezoelectric drive of claim 2, wherein thedrive has three resonators arranged so the contacting portion of eachresonator drivingly engages the driven element and the resonators arealigned tangentially to that driven element.
 19. The piezoelectric driveof claim 18, wherein the three resonators are equally spaced about thedriven element, as are the contacting portions associated with eachresonator.
 20. The piezoelectric drive of claim 18, wherein the threeresonators are coplanar.
 21. A piezoelectric drive for moving a drivenelement, not including the driven element, comprising: a piezoelectricelement driving a resonator, the resonator having a contacting portionfor interactive connection with the driven element during use of thedrive, the contacting portion being located on an edge of a distal endof the resonator, the resonator having an asymmetric placement of thepiezoelectric element relative to the resonator with the massdistribution between the piezoelectric element and the contactingportion being different than the mass distribution of the remainder ofthe resonator.
 22. A method for driving a driven element, said methodcomprising the steps of: placing a piezoelectric element of a resonatorinto a first and/or second oscillation to oscillate a resonator, theresonator having a contacting portion located to interactively engagethe driven element during use, elastically holding the resonatorrelative to the driven element using a spring fastened to at least oneof the resonator and piezoelectric element, the spring located andconfigured to resiliently maintain contact between the resonator and thedriven element; exciting oscillation of the contacting portion of theresonator in two dimensions by applying to the piezoelectric element afirst single frequency with a single phase sufficiently close to aresonant frequency to cause the movement; and exciting oscillation ofthe contacting portion of the resonator in two dimensions by applying tothe piezoelectric element a second single frequency with a single phasesufficiently close to a different resonant frequency to cause adifferent movement of the driven element.
 23. A piezoelectric drive formoving a driven element, comprising: a piezoelectric element separatefrom and drivingly connected to a resonator, the resonator being formedof a single piece of material and having opposing ends, the resonatorhaving a contacting portion in interactive connection with a drivenelement to move the driven element during use of the drive, wherein thedriven element has a cylindrical surface and the resonator has acontacting portion in interactive connection with the cylindricalsurface to rotate the driven element; and a spring connected to theresonator between the ends and spaced apart from the ends a distance,the spring resiliently holding the resonator with respect to the drivenelement, wherein the spring fastens to both the resonator and thepiezoelectric element.
 24. A piezoelectric drive for moving a drivenelement, comprising: a piezoelectric element separate from and drivinglyconnected to a resonator, the resonator being formed of a single pieceof material and having opposing ends, the resonator having a contactingportion in interactive connection with a driven element to move thedriven element during use of the drive; and a spring connected to theresonator between the ends and spaced apart from the ends a distance,the spring resiliently holding the resonator with respect to the drivenelement, wherein the driven element has a cylindrical surface and theresonator has a contacting portion in interactive connection with thecylindrical surface to rotate the driven element and wherein theselected contacting portion is at one end of the resonator and the massof the resonator between the piezoelectric element and the contactingportion is greater than the mass of the resonator between thepiezoelectric element and the other end of the resonator.
 25. Apiezoelectric drive for moving a driven element, comprising: apiezoelectric element separate from and drivingly connected to aresonator, the resonator being formed of a single piece of material andhaving opposing ends, the resonator having a contacting portion ininteractive connection with a driven element to move the driven elementduring use of the drive; and a spring connected to the resonator betweenthe ends and spaced apart from the ends a distance, the springresiliently holding the resonator with respect to the driven element,wherein the selected contacting portion is at one end of the resonatorand the mass of the resonator between the piezoelectric element and thecontacting portion is less than the mass of the resonator between thepiezoelectric element and the other end of the resonator.
 26. Thepiezoelectric drive of claim 1, wherein the contacting portion is on anedge of a distal end of the resonator.
 27. The piezoelectric drive ofclaim 21, wherein the contacting portion is on an edge of a distal endof the resonator.
 28. The piezoelectric drive of claim 22, wherein thecontacting portion is on an edge of a distal end of the resonator. 29.The piezoelectric drive of claim 1, wherein the contacting portion islocated adjacent to the distal end.
 30. The piezoelectric drive of claim21, wherein the contacting portion is on an edge of a distal end of theresonator.
 31. The piezoelectric drive of claim 22, wherein thecontacting portion is on an edge of a distal end of the resonator.